Python Full Course for Beginners [2025]

[Music]

welcome to the complete python Mastery

course in this course you're going to

learn everything about python from

Basics to more advanced concepts so by

the end of the course you'll be able to

confidently use Python for AI machine

learning web development and automation

if you have been looking for a

comprehensive easy to follow well

organized and practical course that

takes you from Zero to Hero this is the

right python course for you you don't

need any prior knowledge of python to

get started I will explain everything

step by step in simple terms so you can

build a solid foundation I'm m hamadani

a software engineer with over 20 years

of experience and I've taught Millions

how to code and become professional

software Engineers through my YouTube

channel and online school quote withm

mar.com if you're new here make sure to

subscribe as I upload new videos all the

time now let's jump in and get

[Music]

started in this course you're going to

learn everything you need to get started

with python just be aware that I've

designed this course for beginners so if

you have some programming experience

check out my other python course for

developers you can see the link on the

top right corner of this video so python

is the world's fastest growing and most

popular programming language not just

amongst software developers but also

amongst mathematicians data analysts

scientists accountants Network engineers

and even kids kids in fact it's the

ideal programming language to learn

first but what makes python so special

here are six reasons with python you can

solve complex problems in less time with

fewer lines of code than many other

languages that's why huge companies like

Google Spotify Dropbox and Facebook have

embraced this beautiful and Powerful

language here is an example let's say we

want to extract the first three

characters of the text hello work this

is the code we would have to write in C

this is how we would do this in

JavaScript and here's how we would do it

in Python see how clean and simple the

language is and that's just the

beginning python is a multi-purpose

language and you can use it for a wide

range of jobs such as data analysis Ai

and machine learning writing automation

scripts building web mobile and desktop

applications as well as software testing

or even hacking so if you want a

high-paying long lasting career in any

of these areas especially Ai and machine

learning python is the language to put

those opportunities at your fingertips

in fact according to indeed.com the

average salary of a python developer in

the US was over

$115,000 in March 2018 and here are four

more reasons that make python the most

desirable language python is a highle

language so you don't have to worry

about complex tasks such as memory

management as you do in

C++ it's crossplatform which means we

can build and run python apps on Windows

Mac and Linux it has a huge community so

whenever you get stuck there is someone

out there to help and it has a large

ecosystem of libraries Frameworks and

tools whatever you want to do it is

likely that someone else has done it

before because because python has been

around for over 20 years there are two

versions of python out there python 2

which is the Legacy version of python

and is going to be supported until year

2020 and Python 3 which is python for

the future in this course you're going

to Learn Python 3 hi my name is msh

hamadani and I'm going to be your

instructor in this course I'm a software

engineer with 18 years of experience and

I've taught way over a million people

how to codee or how to become top

professional software Engineers to learn

more about me and my courses head over

to Cod with.com all right now let's get

started all right the first thing I want

you to do is open your browser and head

over to python.org on this page under

downloads you can download the latest

version of python at the time of this

video the latest version is python 3.13

chances are in the future when you're

watching this video there is a new newer

version of python available don't worry

what I'm going to show you in this

tutorial will apply to Future versions

of python as well so go ahead and

download the latest

version now if you're on windows before

you click install make sure to check

this little box here that says add

python to path this step is very

important and it will save you a lot of

headaches later so check this box and

follow the

installation now to verify that python

is successfully installed click this

magnifier and and here in this search

bar type

terminal now here in the terminal window

type python D- version this verifies

that we have successfully installed

python

3.13 now if you're on Mac press command

and space to bring up the spotlight

search here type

terminal now to verify that we have

installed python correctly on Mac we

should type Python 3

space-- version

so as you can see I've successfully

installed python 3.13 on this

machine so this environment you see here

is what we call python interpreter which

is basically a program that executes

python code we can type our python code

in a file and give it to this

interpreter or we can type our code

directly here in this interactive shell

so here we can write an expression like

two + 2 in programming an expression is

a piece of code that produces a value so

here when we add 2 + 2 we get a value

that is why we refer to this piece of

code as an expression so enter we get

four let's try a different kind of

expression let's see if two is greater

than one we get true which is an example

of a Boolean value you're going to learn

about these Boolean values in the next

section now what if we type two is

greater than five enter we get false so

in programming we have true and false

which are similar to yes and no in

English now what if we type two is

greater than but we don't add a second

value here just press

enter we get a syntax error in

programming syntax means grammar so just

like we have the concept of grammar in

the languages that we speak we have the

exact same concept in programming if we

write a sentence that is not

grammatically correct chances are some

people may not understand that sentence

so in this example we have this

expression which is incomplete it

doesn't have the right grammar or syntax

that is why python interpreter is

complaining by returning an error so

this interactive shell is a great way to

quickly experiment with a bit of python

code but that's not how we build real

world applications to do that we need a

code editor and that's what I'm going to

show you in the next lecture

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when it comes to typing python code you

have two options you can use a code

editor or an IDE which is short for

integrated development environment an

IDE is basically a code editor with some

fancy features like autoc completion

which means as you type code this

feature helps you complete your code so

you don't have to type every character

by hand it's a per activity boosting

feature it also gives you additional

features like debugging which means

finding and fixing bugs in your programs

testing and so on for both code editors

and Ides there's so many options out

there the most popular code editors are

vs code atom and Sublime you can use the

code editor that you prefer in terms of

the Ides again there are so many options

out there the most popular one is pie

charm in this course I'm going to use vs

code or Visual Studio code because

that's my favorite code editor later in

the course I will show you how to

install a Plugin or an extension that

will convert vs code to a powerful ID so

before going any further head over to

code. visual studio.com and download the

latest version of vs

code now with vs code open on the top

from the file menu go to to

open and somewhere on your disk create a

new

folder let's call this folder hello

world and then open it beautiful now

click this icon on the top this opens up

the Explorer panel in this panel you can

see all the files and folders in your

project so let's add a new file and call

that

app.py so all our python files should

have the p my extension press enter now

let's close

this and type a bit of python code in

this lecture we're going to use one of

the built-in functions in Python called

print so in Python we have a lot of

buil-in functions for performing various

kinds of tasks for example as a metaphor

think of the remote control of your TV

on this remote control you have a bunch

of functions like turn on turn off

change the channel change the volume and

so on these are the build buin functions

in your TV we have the same concept in

Python and many other programming

languages so one of these built-in

functions that comes with python is

print and we can use this to print

something on the screen now whenever you

want to use a function you should open

and close parentheses in programming we

say we're calling the print function

calling a function means executing it

now let's display the hello world

message on the screen whenever you want

to work with text you should put your

text in between quotes either double

quotes or single quote now I'm going to

go with double quote and add hello

world and then put a happy Persian cat

here beautiful save the changes with

command and s on Mac or control and S on

Windows now to execute this code we need

to go back to command prompt on Windows

or terminal on Mac but the good news is

that we don't have to switch programs

here in vs code we have an integrated

terminal so press control and back tick

that is the key before number one on

your keyboard that is just below the

escape

button so this is our integrated

terminal now if you're on Windows type

python if you're on Mac or Linux type

Python 3 and next to that add the name

of our file that is app p and here's our

hello word message in the terminal

beautiful now let's take this to the

next level and make it a little bit more

interesting let's close this terminal

window by pressing control and back tick

and add a second line of code so one

more time

print this time let's add quotes with a

star in between them now let's say you

want to repeat this star 10 times so

here we can multiply this is by 10 save

the changes open up the terminal and run

our

program and you can see this star is

repeated 10

times so as you see the instructions in

our program are executed from top to

bottom in order in the next lecture I'm

going to show you how to convert this vs

code to a powerful IDE for building

python applications

[Music]

in this lecture I'm going to show you

how to convert vs code to a powerful IDE

by using an extension called python with

this extension or plug-in we get a

number of features such as linting which

basically means analyzing our code for

potential errors we also get debugging

which involves finding and fixing errors

we'll look at this later in the course

we also get autoc completion which

basically helps us write code faster so

we don't have to type every character we

get code formatting which is all about

making our code clean and readable just

like how we format our articles

newspapers books to make them clean and

readable we get unit testing which

involves writing a bunch of tests for

our code we can run these tests in an

automated fashion to make sure our code

is behaving correctly and finally we get

code Snippets which are reusable code

blocks that we can quickly generate so

we don't have to type them all by hand

now don't worry about memorizing any of

these as we go through the course you're

going to learn about these

features so back to vs code on the left

side click this icon this opens the

extensions panel where we can install

additional extensions to enhance vs code

up here in the search bar search for

python all right look we have an

official extension for python from

Microsoft so go ahead and install this

now you might see a box here saying

reload if you see that make sure to

click it to reload vs code now with this

extension installed we have a ton of new

functionality in vs code for writing

python code the first one I'm going to

show you in this lesson is the ability

to run our code so back to app.py look

with this extension installed now we

have this play icon on the top for

running our code so if we click it we

can see the output of our program in the

terminal window

in this lecture I'm going to show you

linting and action so let's start by

writing some invalid code like this

print space with no parenthesis and then

hello world earlier I told you that

print is a built-in function and

whenever you want to use or call a

function you should always use

parenthesis now to be more precise this

is actually valid python 2 code but

because we're using Python 3 here this

is invalid code from python 3's point of

view so now when I save the changes you

can see this red underline here let's

hover our Mouse over this underline you

can see this tool tip it's coming from

Pilot and here's the error message

missing parenthesis in call to print did

you mean print with parenthesis so this

is the benefit of lenting as you're

writing code you can see potential

problems in your code you don't have to

wait to run your program to see these

errors

so now if we put parenthesis here and

save the changes you can see that red

underline is gone let's look at another

error let's type two plus and then save

the changes earlier we run this code in

Python interpreter's interactive shell

there we got a syntax or grammar error

so if you hover your mouse here one more

time you can see pilent is telling us

that this is invalid syntax or invalid

grammar it's like an incomplete sentence

so this is linting an action now let me

show you a couple useful shortcuts here

on the top look at the view menu here we

have this problems menu look at the

shortcut on Mac it's shift command and M

on Windows it's probably shift control M

so as you're working with vs code try to

memorize these shortcuts because they

really help you write code faster

now let's take a look at this problems

panel so this problems panel lists all

the issues in your code in one place so

if you have an application with multiple

files this is really useful because some

of those files may not currently be open

so this linter pilent will analyze all

your files and if it finds any issues it

will list them here in the problems

panel now you can also put this on the

right side of the screen so let's put it

here so so as you write code these

problems will appear here now let's fix

this issue so I'm going to add three

here save the changes and you can see

the problem disappeared and one last

thing before we finish this lecture once

again on the top let's go to the view

menu the first item is command pallet

this is a very important feature in vs

code once again look at the shortcut

that is shift command and P on Mac or

shift control p on Windows

with this command pallet you can execute

various commands in vsod if you type

lint here you can see all commands

related to linting as you can see all

these commands are prefixed with python

because these commands come with the

python extension that we installed

earlier so these are additional features

available to us in vs code the First

Command here is Select

linter in this list you can see various

linters available for p pent so as

you're reading tutorials or talking to

other people you will hear about linters

such as flake 8 my pie pep 8 and so on

different developers prefer different

linters I personally prefer py lint that

is the most popular one and that is the

default linter set and the python

extension of vs code if you're

adventurous you can try using other

linters on your own the difference

between these linters is in how they

find and Report errors some error

messages are more meaningful or more

friendly the others are more ambiguous

so that's all about linting in the next

lecture we'll talk about formatting

code in Python Community we have a bunch

of documents called python enhancement

proposals or peps here on Google if you

search for python

peps you can see the list of all these

PS

under python.org

sdev peps let's have a quick look

here so here are the peps you can see

each pep has a number and a title the

one that is very popular amongst python

developers is Pep 8 which is a style

guide for python code a style guide is

basically a document that defines a

bunch of rules for formatting and

styling our code if you follow these

conventions the code that you right will

end up being consistent with other

people's code now if you have time you

can go ahead and read this pep eight

documentation but if not don't worry

because throughout this course I'm going

to explain the key things in pep 8 in

this lecture I'm going to show you a

tool that helps you automatically format

your code according to pep

8 so back in vs code let's write some

python code x equal 1 here I'm declaring

a variable and setting it to one if if

you're not familiar with variables don't

worry in the next section you're going

to learn about them so according to pep

8 this code is considered ugly because

by convention we should add a space

around this equal sign or the assignment

operator now since you're starting out

with python you probably don't know

these rules so let me show you a tool

that helps you automatically format your

code let's revert this back to its

original state now we need to go back to

the command pallet remember so it's

right here under View and the shortcut

is shift command and

P here if you search for format you can

see this command format document the

first time you execute this command

you're going to see this message here

formatter autopep8 is not installed so

there are a bunch of tools for

formatting python code the most popular

one is Auto Pep 8 and this is the tool

that this python extension we installed

uses to format our our code now if you

don't see this you can install autopep8

using the extensions panel so once again

on the left side click this icon and

search for Auto Pep

8 there it is let's install

it good so let's go ahead and install

this good now one more time let's open

up the command pallet and execute format

document

see this tool automatically formats our

code beautiful let's take a look at

another example I'm going to declare

another variable Y and set it to two and

a variable with a long name like unit

underline price and we set this to three

now some developers have this habit of

formatting their variable declarations

like this so they put all

these equal signs in the same column

according to pep 8 this is considered

ugly so once again let's format our code

that is better beautiful now let me show

you a trick opening up this command

palet and searching for format document

every time is a little bit timec

consuming so I'm going to show you how

to have your file automatically

formatted as soon as you save the

changes on the top let's go to the code

menu preferences and

settings here in the search box search

for for format on

save so we have this option editor

format on Save take this now back to

app.py I'm going to change the

formatting of these lines make them

really ugly now as soon as I save the

changes you can see my code is

reformatted

[Music]

beautiful all right now let's talk about

a few different ways to run python code

as I told you before one way to run

python code is by opening the terminal

window if you're on Windows type python

if you're on Mac type Python 3 followed

by the name of the file this approach is

useful in situations where you don't

have access to a code editor okay now

with the python extension in vs code

there is a simpler way to run python

code we get this play button on the top

when we click it we see the output in

the terminal but clicking this button

every time we change our code is a

little bit tedious so let me show you

how to associate a shortcut to this

button first we close this next we bring

up the command pallet the shortcut on

Mac is shift command and P on Windows is

shift control

P here we search for open keyboard

shortcuts look we have this command up

here now on this window we can see all

the commands in vs code and the

shortcuts associated with them here in

the search bar search for run python

file okay so this is the command that is

associated with the play button as you

can see we don't currently have any key

bindings or shortcuts here so double

click in this column now here you can

press any key combination for creating a

shortcut I'm going to press controll and

R okay now we press enter with this in

place we can go back to app.py and press

controlr and here we see the out

beautiful when we talk about python we

mean two separate things that are

closely related Python language and a

particular implementation python as a

language is just a specification that

defines a set of rules and grammar for

writing python code a python

implementation is basically a program

that understands those rules and can

execute python code earlier in the

course we downloaded python from py

python.org this is the default

implementation of python called cpython

It's a program written in C that's why

it's called C python so here in terminal

when we run python we get this C python

this is the default implementation of

python there are a few other

implementations out there such as jython

written in Java iron python written in C

and piie written in a subset of python

itself as new features are added to the

the Python language they are first

supported by cpython because that's the

default implementation and then they

will gradually come to the other

implementations in theory if we give

some python code to any of these

implementations we should get the same

result but in practice that's not always

the case certain features may be

available in one implementation but not

another or they may just behave a little

bit differently in a particular

implementation now you might ask what is

the point of this why do we have several

implementations of python wouldn't C

python be enough well it's for the same

reason that we have multiple operating

systems or multiple browsers or multiple

programming languages after all these

years we programmers haven't agreed on a

single programming language and that's

the same story with python

implementations however there is one

technical reason behind these

implementations that you should be aware

of since jyon is implemented in Java it

allows you to reuse some existing Java

code in a Python program so if you're a

Java developer and you want to import

some Java code into a Python program you

should use jython instead of

cpython similarly iron python is written

in C so if you're a c developer and want

to bring some C code into a Python

program you will have to use iron python

next we'll look at how exactly cpython

executes python code

[Music]

the programming languages we use like C

C Java python these are all Simple Text

based languages that we humans

understand computers don't understand

them they only understand machine code

so if we have some code written in C we

should convert it to machine code and

that's the job of a c compiler so a c

compiler is a program that knows how to

convert or compile C code into machine

code however this machine code is

specific to the type of CPU of a

computer so if we compile a c program on

a Windows machine we can't execute it on

a Mac because Windows and Mac have

different machine code just like how

people from different countries speak

different languages Java came to solve

this problem Java compiler doesn't

compile Java code into machine code

instead it compiles it into a portable

language called jav Java bite code which

is not specific to a hardware platform

like Windows or Mac now we still need to

convert Java bite code to machine code

so Java also comes with a program called

Java virtual machine or jvm for doing

this when we run a Java program jvm

kicks in it loads our Java bite code and

then at runtime it will convert each

instruction to machine code with this

model we can run Java bite code on any

platforms that have a jvm we have jvm

implementations for Windows Mac and so

on so the jvm implementation on Windows

knows how to convert Java bite code into

machine code that a Windows machine can

understand C and python have also taken

the same route so they are platform

independent when we run a Python program

using cpython first it will compile our

python code into python bite code then

it will pass that bite code to python

virtual machine which will in turn

convert it into machine code and execute

it this is how cpython works in the last

lecture we talked about various python

implementations I told you that if you

want to reuse some Java code in a Python

program you should use jython now let's

see how jython makes this possible when

you use jython to run a Python program

instead of compiling your python code

into python by code it will compile it

to Java by code so we can take this Java

bite code and run it using Java virtual

machine and that's why you can import

some Java code into a Python program

when using jython because the end result

is Java bite code which will eventually

be executed by Java virtual

[Music]

machine so I've got a few questions for

you cuz I want to see if you have been

really paying attention to this video or

not you better have so here's the first

question for for each question I want

you to pause the video think about the

answer for a few seconds when you're

ready continue watching so here's the

first question what is an

expression an expression is a piece of

code that produces a value here's an

example of an expression what do you

think is the value of this

expression well here we have this string

we're multiplying this by three so the

result will be a string of three

asterisk

like this here's another question what

is a syntax

error a syntax error is a kind of error

that is due to bad syntax or bad grammar

in the code and finally the last

question what does a linter

do a linter is a tool that checks our

code for potential errors mostly in the

category of syntactical Errors so if you

have grammatical issues in our code the

linter will tell us before running our

program okay okay that's it for now if

you like more quizzes and programming

exercises look at the link below this

video and if you have enjoyed this video

I hope you have please support me by

giving a thumbs up please like this

video and share it with others in the

next section we're going to look at the

fundamentals of

[Music]

python hey guys I just wanted to let you

know that this tutorial is actually the

first two hours of my complete python

Mastery course if you're finding this

helpful and want to dive even deeper the

the full course covers everything from

beginner Basics to advanced concepts

like machine learning web development

and automation you'll also get Hands-On

projects to build your skills step by

step I put the link in the description

box if you're ready to take your python

knowledge to the next level now let's

continue let's start this section by a

discussion of variables which are one of

the Core Concepts in programming we use

variables to store data in computer's

memory here are a few examples I'm going

to Define a variable called students

underline count and setting it to a

th000 when we run this program python

interpreter will allocate some memory

and store this number thousand in that

memory space then it will have this

variable reference that memory location

so this variable is just like a label

for that memory location we can use this

variable or this label anywhere in our

program program to get access to that

memory location and the data stored

there so now if we print students count

and run our program we will get the

number thousand so this is the basic of

variables now what kind of data can we

store in computer's memory well we have

several different kinds of data in this

section we're going to look at the

built-in primitive types in Python

primitive types can be numbers

booleans and strings let me show you so

here we have a whole number we refer to

this as an integer in programming we can

also have numbers with a decimal point

let's take a look so rating we set this

to

4.99 this is what we call a float or a

floating Point number and this

terminology is not specific to python in

the future when you learn a new

programming language you're going to

hear these terms again now let's take a

look at an example of a

Boolean is published we set this to true

or false these are examples of Boolean

values in programming so Boolean values

can either be true or false and these

are exactly like yes and no in English

later in the course you will learn that

we'll use these Boolean values to make

decisions in our programs for example if

the user is an admin user perhaps we

want to give them extra

permissions so these are the Boolean

values now take into account that python

is a case sensitive language which means

lowercase and uppercase characters have

different meanings so Boolean values

should always start with a capital

letter like what you see here if we type

false or false these are not accepted

Boolean values in Python only what you

see here is a valid Boolean value so

false or true and finally let's take a

look at an example of a string so of

course underline name we set this to a

string like Python Programming so a

string as I told you before is like text

whenever you want to work with text in

your programs you need to surround your

text with quotes so these are the basics

of

variables so these are the variables

from the last lecture now I've got a

question for you there are four things

that I've consistently used in this

program can you spot them if you want

you can pause the video think about this

for a few seconds and then continue

watching so here are those four things

the first thing is that all my variable

names are descriptive and meaningful so

students count represents the number of

students for a course or course name

clearly explains that this variable

holds the name of a course one of the

issues that I see a lot amongst beginner

programmers is that they use mystical

names for their variables something like

this CN as in short for course name when

someone else reads this code they have

no idea what CN stands for or they use

variable names like C1 when I look at

that code I wonder where is C2 and what

is the difference between C1 and C2 so

these variable names are very mystical

that's a bad practice make sure your

variable names are always descriptive

and meaningful because this makes your

code more maintainable now there are

times that you can use short variable

names like x y z if you're dealing with

things like coordinates so that's an

exception now the second thing that I

have consistently used in this code is

that I have used lowercase letters to

name my variables so here we don't have

course name all in capital or in title

case all letter are lowercase right

let's delete this the third thing that

I've consistently used here is that I

have used an underscore to separate

multiple words and I've done this to

make my variable names more readable

because in Python we cannot have a space

in variable names so we cannot have

course name and if you put these two

words together it's a little bit hard to

read that's why we use an underscore and

the fourth thing that I have used

consistently here is that I have put a

space around this equal sign again

that's one of the issues I see a lot

amongst beginners they write code like

this this is a little bit ugly this is

what we call Dirty code dirty stinky

smelly you should write code that is

clean and beautiful so other people can

read it like a story like a newspaper

article it should be formatted properly

and that's why we have pep 8 in Python

now the good thing is if you forget

these rules when you save the changes

autopep8 kicks in and it automatically

reformats your code but that aside you

should always give yourself the habit of

writing clean code without relying too

much on the tooling so these are all the

best practices about naming your

variables next we're going to look at

strings in more

detail so here we have this course

variable set to Python Programming as I

told you before whenever you work with

text you should surround your text with

quotes you can either use double quotes

or single quotes that's more of a

personal preference but quite often we

use double quotes we also have triple

quotes and we use them to format a long

string for example if you have let's say

a variable message that is the message

we want to include in the body of an

email you can use triple quotes to

format it like this hi John this is msh

from code with m.com blah blah blah so

that's when we use triple codes now we

don't need this in this lecture so

delete let me show you a few useful

things you can do with strings first of

all we have this built-in function in

Python for getting the length of strings

what is a function a function is

basically Bally a reusable piece of code

that carries out a task as a metaphor

think of the remote control of your TV

on this remote control you have buttons

for different functions like turn on

turn off change the channel and so on

these are the built-in functions in your

TV in Python and many other programming

languages we have the exact same concept

so we have functions that are built into

the language on the platform you can

reuse these functions to perform various

tasks so here we can use the built-in

Len function to get the length of a

string which means the number of

characters in that string now whenever

you want to use a function you should

use

parenthesis now we say we're calling

this function which basically means

we're using this function now some

functions take additional data which we

refer to as arguments these arguments

are inputs to these functions so this

Len function takes an input or an

argument here we pass our course

variable and this will return the number

of characters in this string so let's

print that and see what we get run the

program we get 18 because we have 18

characters here let's look at another

example if you want to get access to a

specific character in this string you

use the square bracket notation so here

we add course square bracket brackets to

get the first character you use the

index zero so in Python like many other

languages strings are zero index which

means the index of the first character

or the first element is zero so now when

we print

this we'll get P okay now you can also

use a negative index like minus1 what

does that mean well if zero represents

the first character here what do you

think negative 1 represents that takes

us back to the end of the string so that

Returns the first character from the end

of the string let's draun this program

you will see we'll get

G there you go using a similar syntax

you can slice strings let me show you so

I'm going to duplicate this line and

remove

ne1 now let's say we want to extract the

first three characters in this string so

here we need two indexes the start index

colon the end index so this will return

a new string that contains the first

three characters in this course variable

that would be P Y and T so the index of

these characters are zero 1 and two so

that means the character at the end

index is not included okay let's run the

program and make sure we get the right

result there you go

PYT now what if we don't include the end

index what do you think we're going to

get it's Common Sense we start from

index zero and go all the way to the end

of the string so this will return a new

string that is exactly the same as the

original string let's take a

look so we get Python programming

now what if we don't include the start

index but include the end index what do

you think we're going to get once again

it's common sense so by default python

will put zero here so it will start from

the beginning of the string so when I

run this program we should get PYT one

more time there you

go and finally as the last example if we

don't include the start and the end

Index this will return a copy of of the

original string let's look at this so we

get Python

Programming now you don't have to

memorize any of these just remember we

use the Len function to get the length

of a string we use bracket notation to

get access to a specific element or a

specific character and we use this

notation to slice a

string so we have this string here

python Pro programming now let's say we

want to put a double quote in the middle

of this string there is a problem here

python interpreter sees this second

string as the end of the string so the

rest of the code is meaningless and

invalid how do we solve this problem

well there are two ways one way is to

use single Cotes for our string and then

we can use a double code in the middle

of the string but what if for whatever

reason perhaps for being consistent in

our code we decided to use double quotes

how can we add another double code in

the middle of this string well we can

prefix this with a backs slash backslash

in Python strings is a special character

we have a jargon for that called Escape

character we use it to escape the

character after let me show you what I

mean so let's let's print this course

and run this

program what's going on here we don't

have the backs slash because we use that

to escape this double code and basically

display it here so backs slash is an

escape character and back SL double

quote is an escape sequence in Python

strings we have a few other Escape

sequences that you should be aware of

let me show you so in Python we use a

hash sign to indicate a comment a

comment is like additional note that we

add to our program it's not executed by

python interpreter okay so here are the

Escape sequences you have seen back SL

double quote we also have back SL single

code so we can use that to add a single

code here let's run the program here it

is

beautiful we also have double backs

slash so if you want to include a

backslash in your strings you should

prefix it with another backslash let me

show you so when we run this we get

python one back slash

programming and finally we have back sln

which is short for new line so now if I

add a back slash n here see what we

get we get a new line after python so

programming will end up on the second

line so these are the Escape sequences

in

Python here we have two variables first

and last let's say we want to print my

full name on the console so we can

Define another variable full set it to

first then concatenate it with a space

and one more time concatenate it with

last now when we print full

we get my full name on the console

beautiful now this approach of using

concatenation to build a string is okay

but there is a better and newer approach

we can use formatted strings so here we

can set full to this string and prefix

it with an F which can be lowercase or

uppercase this formatted string doesn't

have a constant value like these two

strings here It's actually an expression

that will be evaluated at runtime so

here we want to add our first name we

use curly braces to print the value of

the first variable after that we add a

space and then we add curly braces one

more time to print the last name so at

run time this expression will be

evaluated what we have in between curly

braces will be replaced at runtime

now let's run this program one more time

we get the exact same result just be

aware that you can put any valid

expressions in between curly braces so

earlier you learned about the built-in

Len function we can call Len here to get

the length of this string let's run this

program one more time so we get

four we can also replace last with an

expression like this 2 + 2 let's run

this program we get four and four so

when using formatted strings you can put

any valid expressions in between curly

braces in this lecture we're going to

look at a few useful functions available

to work with strings so earlier you

learned about this builtin Len function

this function is general purpose so it's

not limited to Strings later I will show

you how to use this function with other

kind of objects but in Python we have

quite a few functions that are specific

to a strings let me show you so here if

we type course dot see all these are

functions available on strings now in

precise terms we refer to these

functions as methods this is a term in

object-oriented programming that you

will learn about later in the course for

now now what I want you to take away is

that everything in Python is an object

and objects have functions we call

methods that we can access using the dot

notation so here course is an object we

use the dot notation to access its

functions or more accurately methods

let's take a look at a few of these

methods we have upper to convert a

string to uppercase now let's print this

and run the program

here's what we get beautiful now note

that the methods that you call here

return a new string so the original

string is not affected let me show you

so print course run the program one more

time look this is our original string

right so course. upper returns a new

string a new value we can store it in a

variable like course underline

Capital like this now to keep this demo

simple and consistent I'm going to

revert this back and use a print

statement we also have the lower method

to convert a string to lowercase we also

have title which will capitalize the

first letter of every word so if our

string was like this when we call the

title method we get Python Programming

as you see here okay

another useful method is strip and we

use it to trim any white space at the

beginning or end of a string this is

particularly useful when we receive

input from the user let me show you so

let's

imagine the user entered a couple of

white spaces at the beginning of this

string when we call course. strip those

white spaces will be removed take a look

so note that in the first three examples

we have the those white spaces but in

the last one it is removed so a strip

removes the white space from both the

beginning and end of a string we also

have l strip which is short for left

strip and R strip which is short for

Right strip so it will remove the white

space from the end of a string if you

want to get the index of a character or

a sequence of characters in your string

you should use the find method and me

show you so of course

find so as an argument here we pass

another string we can pass a character

or a series of characters let's find the

index of

Pro run the program so the index of pro

is nine so if we start from zero here

all the way to nine this is the index of

pro okay now as I told you before python

is a case sensitive language so if I

pass a capital P here obviously we don't

have these exact characters in our

string so let's see what we get we get

-1 that means this string was not found

in the original

string another useful method is replace

so we call replace with this we can

replace a character or a sequence of

characters with something else so let's

say we want to replace all lowercase P's

with

J with this we

get jython durog gramming whatever that

means and finally if you want to check

for the existence of a character or a

sequence of characters in your string

you can use the in Operator Let Me Show

You So

print we write an expression like this

Pro in

course so this is an expression as I

told you before an expression is a piece

of code that produces a value so this

expression checks to see if we have Pro

in course the difference between this

expression and calling the fine method

is that the fine method Returns the

index of these characters in our string

but as this expression returns a Boolean

so it's a true or false let me show you

so run the

program we get the Boolean

true and finally we have the not

operator and we use that to see if our

string does not contain a character or a

sequence of characters

so let's change this to

Swift not in course when this expression

is evaluated what do you think we're

going to get well we don't have Swift in

this string so not in will return true

let's take a look there you go

go so these are the useful string

Methods next we'll look at

numbers in Python we have three types of

numbers two of these you have already

seen before they are integers and floats

we also have complex numbers so complex

numbers in math are in the form a plus b

i where I is the imaginary number number

now if you're not familiar with this

concept don't worry this is something

that is used a lot in mathematics and

electrical engineering if you want to

use Python to build web applications

you're never going to use complex

numbers but let me quickly show you the

Syntax for representing complex numbers

instead of I we use J so here is an

example 1 + 2 J so X now is a complex

number and by the way as I told you

before this is just a common or an

additional note in our program when we

run this program anything after this H

sign will be ignored so these are the

three types of numbers we have in Python

for all these types of numbers we have

the standard arithmetic operations that

we have in math let me show you so we

have

addition

subtraction

multiplication division but we actually

have two different types of divisions

let me show you first let's run this

program so with this division operator

which is a slash we get a floating Point

number if you want an integer you use

double slashes let me show

you so double slash run the

program we get three okay we also have

modulus which is the remainder of a

division and finally exponent Which is

less left to the power of right so 10 to

the power of 3 will be a th000 these are

the standard arithmetic operators now

for all these operators we have a

special operator called augmented

assignment operator let me show you so

let's imagine we have X set to 10 we

want to increment X by let's say three

we can write an expression like this x =

x + 3 or we can use an augmented

assignment operator that is a little bit

shorter so we write X+ equal three these

two statements are exactly the same now

here I'm using addition as an example

you can use any of these operators

here next I'm going to show you some

useful functions to work with

numbers in this lecture we're going to

look at a few few useful functions to

work with numbers so we have this

built-in function round for rounding a

number so if we pass 2.9 here and print

the result we will get three we have

another useful built-in function called

ABS which Returns the absolute value of

a number so if we pass -2.9 here we'll

get positive 2.9 now teic we have only a

handful of built-in functions to work

with numbers if you want to write a

program that involves complex

mathematical calculations you need to

use the math module a module is like a

separate file with some python code so

in Python we have this math module which

includes lots of mathematical functions

for working with numbers but we need to

import this module so we can use it on

the top we type import math now math in

this program is an object so we can use

the dot notation to see all the

functions or more accurately all the

methods available in this object as an

example we have math. seal for getting

the ceiling of a number so if we pass

2.2 here and run this

program we get

three now in this math module we have

lots of functions let me show you how to

find the complete list here on Google

search for Python 3 make sure to add the

version number math

module on this

page you can see all the functions in

the math module so in this lecture we

looked at math. seal we also have math.

copy sign Fabs and so on as an exercise

I encourage you to play with a couple of

functions in this

module all right now let's take a look

at another useful built-in function in

Python we use the input function to get

input from the user as an argument we

pass a string this will be a label that

will be displayed in the terminal you'll

see that in a second so let's add X

colon now this function returns a string

so we can store it in this variable now

let's imagine that y should be x + 1

save the changes now don't run this

program using the code Runner extension

because code Runner by default runs your

program in the output window which is

read only so you won't be able to enter

a value so open up the terminal using

control and backspace once again if

you're on Windows type python if you're

on Mac or Linux Linux type Python 3 and

then

app.py so here's our label let's enter a

value like one we got an error type

error what is going on here well when we

receive input from the user this input

always comes as a string so this

expression at runtime will look like

this string 1 + 1 note that the number

one is different from string one because

these are two different types now when

python sees this expression it doesn't

know what to do because two objects can

be concatenated if they are of the same

type so here we need to convert this

string one to a number in Python we have

a few built-in functions for type

conversion we have int for converting a

number to an integer we have

float we have bull and stir or string

now in this case we don't need to

convert X to a string because X is

already a string if you don't believe me

let me show you so I'm going to comment

out these few

lines now let's

print type of X so type is another

built-in function we pass an object as

an argument and it returns its type also

I'm going to comment out this line

because that's the bad boy we don't want

to execute this save the changes back in

the terminal let's run this program one

more time enter one look this is what

the type function returns now don't

worry about the class we'll talk about

classes later in the course so the type

of X is a stir or

string so let's delete this line to fix

this problem we need to convert X to an

integer and then we can print both X and

Y using a format of string remember so

we add an F quotes right here we add a

label like X then we'll add a field so

here we want to print the value of x

variable after that we add some more

text and finally we want to print the

value of y let's run this program one

more

time so here in the terminal let's enter

one and here's the result X is one and Y

is two beautiful

now all these built-in functions are

self-explanatory the only tricky one is

bull because in Python we have this

concept of truthy and falsey values

these are values that are not exactly a

Boolean true or false but they can be

interpreted as a Boolean true or false

so here are the falsy values in Python

M2 strings are considered falsy so

they're interpreted as a Boolean false

numbers Z is also falsy we have an

object called non which represents the

absence of a value we'll look at this

later in the course so whenever we use

these values in a boan context we get

false anything else will be true let me

show you a few

examples so in this interactive shell in

Python let's

convert number zero to Bull that's falsy

so we get false what about bull of one

we get true if we pass a negative number

we also get true if we pass a number

larger than one like five we still get

true so we only get false when we try to

convert zero to aoia now with strings I

told you that an empty string is falsey

so here we'll get false anything else is

true so even if I have a string that is

false we'll get true because the this is

not an empty string it's a string with a

few characters that's why it's evaluated

as

true all right once again it's time for

another quiz let's see if you have been

really paying attention to this tutorial

so here's the first question what are

the built-in primitive types in

Python we have strings numbers and

booleans numbers can can be integers

Floats or complex numbers here's the

second question you have this variable

fruit set to Apple what do you think we

will see on the terminal when we print

fruit of

one well using screw brackets we can

access individual characters the index

of the first character is zero so this

expression Returns the second character

which is p what if we add a colon and

negative one

here well using the syntax we can slice

a string our start index is one and our

end index is negative -1 which refers to

the first character from the end of the

string now when slicing a string the

character at the end index or1 is not

included so with this expression we'll

get all the characters starting from the

second character which is p all the way

until we get to e so the result of this

expression is PPL L here's another

question what is the result of this

expression well this is what we call the

modulus operator and it Returns the

remainder of a division which is in this

case

one and finally the last question what

do you think we will see when we print

bull of

false well earlier I told you about

falsy values in Python so number zero an

mty string and the non-ob these are all

falsy values anything that is not falsey

is considered truthy here we have a

string that has five characters it

doesn't matter what those characters are

this is not an empty string so it's not

falsey it's truy so when we convert it

using the bull function we'll get the

Boolean true and this brings us to the

end of the section in the next section

you're going to learn the fundamentals

of computer programming I hope you have

enjoyed this section and thank you for

watching we're going to start this

section by exploring comparison

operators we use comparison operators to

compare values here are a few examples

so 10 is greater than three we get true

so what we have here is a Boolean

expression because when this expression

is evaluated we'll get a Boolean value

that is true or false here is another

example 10 is greater than or equal to

three once again we get true we also

have less than so 10 is less than 20 we

have less than or equal to here's the

equality operator so 10 is equal to 10

what about this expression what do you

think we're going to get we get false

because this values have different types

and they're stored differently in the

computer's memory and finally we have

the not equal operator so now with this

expression we should get true beautiful

we can also use these comparison

operators with strings let me show you

so we can check to see if bag is greater

than and apple we get true because when

we sort these two words bag comes after

so it's considered greater now what

about this one bag equals Capital bag we

get false here's the reason every

character you see here has a numeric

representation in programming let me

show you so we have this built-in

function called or don't worry about

memorizing this because you're probably

never going to use this in the future

but let me show you the numeric

representation of the letter B so that

is 98 in

contrast capital B is represented as

66 that is the reason these two strings

are not equal so these are the

comparison operators in Python next

we'll look at conditional

statements in almost every program there

are times you need to make decisions and

that's when you use use an if statement

here's an example let's say we have a

variable called temperature we set it to

35 now if temperature is greater than 30

perhaps we want to display a message to

the user so we use an if statement if

after if we add a condition which is

basically a Boolean expression an

expression that produces a Boolean value

so if temperature is greater than 30

here we have a Boolean expression if

this expression evaluates to true the

following statements will be executed

let me show you now here's the important

part that a lot of beginners miss when

you use an if statement you should

always terminate your statement with a

colon now let's see what happens when I

press

enter our cursor is indented so here we

have two white spaces this is very

important because using these

indentations python interpreter will

know what statements should be executed

if this condition is true here we want

to print a message like it's warm we can

print another message as well drink

water so we can have as many statements

as we want here as long as they are

indented they belong to this if block

now when we finish here we should remove

indentation to indicate the end of this

if block so here we can add a print

statement with a message like Don this

statement will always be executed

whether this condition is true or not

now note that when I save the changes

this indentation you see here is going

to be doubled up take a look save there

you go so when we save the changes autop

pep 8 reformats our code and uses four

white spaces for indentation so one 2 3

4 it uses four white spaces because

that's what pep 8 recommends

all right now let's run this

program so because temperature is

greater than 30 we see the first two

messages and we see the dawn message

regardless so if I change the

temperature to let's say 15 and run the

program one more time look this Dawn

message is executed whether our

condition is true or not so pay great

attention to these indentations that's

one of the issues I see in beginner's

code let's say they want both these

print statements to be executed if the

condition is true accidentally they

remove the indentation on the fourth

line and that's why their program

doesn't work as they expect so be

careful about this now what if you want

to have multiple conditions we use an L

if statement so L if that is short for

L's if here we can add another condition

another expression so temperature is

greater than 20 one once again colon

enter now by default here vs code is

using two white spaces so don't worry

about this as soon as you save the

changes those two white spaces will be

converted to four white spaces so let's

print a different

message it's

nice save the changes now look all these

lines are indented

consistently you can have as many l

statements as you want and optionally

you can also have an else statement so

if none of the previous conditions are

true then what you have in the else

block will be executed once again we add

the colon annotation

print here we can add a message like

it's

called save the changes in this case

temperature is 15 so none of these two

conditions will be true and we will see

it's called let's run the program there

you go

in this lecture I'm going to show you a

technique for writing cleaner code so

let's say we're building an application

for University and we want to check to

see if the person who's applying for

this University program is eligible or

not so we start by defining a variable

called age set it to 22 now if age is

greater than or equal to 18 colon

print

eligible remove the initation else colon

print not eligible let's run the program

make sure it works beautiful now there

is nothing wrong in this piece of code

but I want to show you a cleaner way to

achieve the same result instead of

having a print statement here we can

define a variable like message and set

it to this string

that is the first step so message equals

this string and then we will

print this

message now when you have an if L

statement with this structure where

you're basically assigning a value to a

variable you can rewrite this in a

simpler way so this is how it works all

we want to do over these VI lines is to

assign a value to this message variable

right so with start with message we set

it to

eligible if age is greater than or equal

to 18 else we set it to not

eligible this statement is almost like

plain English so what we have on line

seven is exactly equivalent to these

four lines of code delete save the

changes run the program you can see this

person is eligible if I change the age

to 12 12 and run the program we get not

eligible so what we have here is called

Turner

operator in Python we have three logical

operators and we use these operators to

model more complex conditions so these

operators are and or and not let's see a

real word example of using these

operators so imagine we're building an

application for processing loans so we

need two variables High income we can

set this to

true and good underlined credit we set

it to true now here's the condition we

want to implement if the applicant has

high income and good credit score then

they are eligible for the loan so if

High income and good credit

we add the colon and print

eligible now note that here I have not

compared the value of this variable with

true that is one of the issues I see in

a lot of beginners code this is

redundant and unprofessional because

High income is a Boolean so it's either

true or false we don't need to compare

true with true so if this condition is

true and this second condition is true

then we will print eligible in the

terminal so save the changes and run the

program obviously this person is

eligible however if one of these

conditions is false we will not see

eligible in the terminal so let's add an

lse statement here and

print not

eligible run the program we see not

eligible so this is how the and operator

works with and operator if both

conditions are true the result will be

true in contrast with the or operator as

long as at least one of the conditions

is true the result will be true so if I

replace and with or here we should see

eligible in the terminal let's run it

one more time there you go so these are

the and and or operators now let's take

a look at an example of the not operator

so I'm going to Define another variable

student set it to True temporarily I'm

going to remove this expression and

simplify it we'll come back to this

later so let's say if the person is

eligible if they are not a student the

not operator basically inverses the

value of a Boolean so in this case

student is true when we apply the not

operator the result will be false so in

this case our condition will be false

and that's why this print statement will

not not be executed let me show you so

save run the program they're not

eligible if student was

false when we apply the not operator

will get true so our condition will be

true and we'll see eligible let's run it

one more time there you go with these

operators we can model even more complex

conditions here's an example a person

can be eligible if they have either High

income or good CR credit and they should

not be a student let me show you how to

implement this condition so if High

income or good credit we want at least

one of these conditions to be true so we

put these in parenthesis we want to

separate these from the other condition

which is not a student now the result of

this should be true which means at least

one of these conditions should be true

after that will add and not

student and finally call so with these

operators you can model all kinds of

real word

scenarios so here's the example from the

last lecture a person is eligible for a

loan if they have high income and good

credit and they're not a student now one

thing you need to know about this

Boolean operator

is that they are short circuit what do I

mean by that well when python

interpreter wants to evaluate this

expression it starts from the first

argument if this is true it continues

the evaluation to see if the second

argument is also true so it continues

the evaluation all the way to the end of

this

expression however as soon as one of

these arguments is false the evaluation

stops let me show you what I mean so if

I change High income to false when

python interpreter sees this expression

it starts here it knows that high income

is false so it doesn't matter what comes

after the result of this entire

expression will always be false because

at least one of the arguments or one of

the operant is false this is what we

call short circuiting just like the

short circuit concept we have in

electronics so the evaluation stops as

as soon as one of these arguments

evaluates to false we have the same

concept with the or operator so if I

change these and operators to or let's

see what happens with the or operator we

know that at least one of the arguments

should be true so the evaluation stops

as soon as we find an argument that

evaluates to true in this case when

python interpreter evaluates this

expression it sees that high income is

false so so it continues the evaluation

hoping that the next argument will be

true here good credit is true so

evaluation stops and the result of this

entire expression will be true so in

Python logical operators are short

circuit in this lecture I'm going to

show you how to chain comparison

operators this is a very powerful

technique for writing clean code here's

an example let's say we want to

implement a rule that says age should be

between 18 and

65 here's how we can implement it so we

Define a variable like AG set it to 22

now if age is greater than or equal to

18 and age is less than 65 then we print

eligible now here's a question for you

how do we write this rule in math we can

write it like this

well more accurately we should have an

equal sign here so age should be between

18 and 65 this is how we write this rule

in math now I've got some good news for

you we can write the exact same

expression in Python so I'm going to

move this up put an if statement here

line four and line three are exactly

equivalent but as you can see line four

is cleaner and easier to read so let's

get rid of line

three this is what we call chaining

comparison

operators all right here's a little quiz

for you I want you to pause the video

and think about this quiz for 10 to 20

seconds what do you think we'll see on

the terminal when we run this program so

pause the video figure out the answer

when you're ready come back continue

watching all right let's see what

happens when we run this program first

we get this if statement in this case

we're comparing two different objects

for equality and these objects have

different types we have a number

compared with a string so number 10 and

string 10 are not equal that is why a

will not be printed on the terminal so

the control moves to the L If part here

we have two Boolean Expressions here's

the first one here's the second one and

they are combined using the logical end

so if both these expressions are

evaluated to true then this entire

expression will be true and we will see

be on the terminal let's see if both

these expressions are evaluated to True

here's the first part bag is greater

than Apple that is true because when we

sort these words bag comes after Apple

but look at the second part part this

expression is evaluated to false because

bag is not greater than cat so when we

apply The Logical end between true and

false the result will be false that is

why this statement will not be executed

so to control moves to the lse part and

when we run this program the letter c

will be printed on the

terminal there are times that we may

want to repeat a task a number of times

for example let's say we send a message

to a user if that message cannot be

delivered perhaps we want to retry three

times now for Simplicity let's imagine

this print statement is equivalent to

sending a message in a real world

program to send a message to a user we

have to write five to 10 lines of code

now if you want to retry three times we

don't want to repeat all that code that

is ugly that's when we use a loop we use

Loops to create repetition so here is

how it works we start with four number

in we have a built-in function called

range now how many times we want to

repeat this task let's say three times

so we call range and pass three as an

argument now similar to our if

statements we need to terminate this

line with a

colon enter we get indentation so in

this block we can write all this

statements that should be repeated three

times let's do a print a message like

attempt save the changes run the program

so we have attempt printed three times

beautiful now what is this number let's

take a look it's a variable of type

integer so let's pass it as the second

argument to the print function number

run the program this is what we get 012

so here we have a for Loop this for Loop

is executed three times in each

iteration number will have a different

value initially it will be zero in the

second iteration it will be one and

finally in the last iteration it will be

two now here we can do something fun we

can

add one to this around the program and

now the messages that we print are kind

of more meaningful or more user friendly

like attempting number one attempting

number two and so on we can take this to

the next level so we can pass another

argument here I'm going to add an

expression one more time number + one so

we'll get 1 2 3 now I want to put this

expression in parenthesis so let's

select this put it in parenthesis and

then multiply it by a DOT so here we

have a string that is multiplied by a

number the result will be that string

repeated that number of times let's take

a look so run the program see that's

pretty cool isn't it now let me show you

one more thing before we finish this

lecture as you saw this range function

generates numbers starting from zero all

the way up to this number here but it

doesn't include this number here we can

pass another argument say start from one

and finish before

four with this change we don't need to

add one to number every time because in

the first ation this number variable

will be set to one so we can simplify

our code and make it

cleaner let's run it one more time we

get the exact same result we can also

pass a third argument as a step so I'm

going to change the second argument to

10 and pass two as a step look at the

result these are the numbers we get 1 3

5 and so on so pretty useful you're

going to use this function a lot in real

world application

continuing with the example from the

last lecture let's imagine the scenario

where after the first attempt we can

successfully send the message in that

case we want to jump out of this Loop we

don't want to repeat this task of

sending a message three times let me

show you how to implement this so in

this demo I'm going to simulate the

scenario where we can successfully send

a message so we Define a variable

successful and set it to

true now here after this print statement

we'll have an if statement if successful

colon then perhaps we can

print

successful now here we want to jump out

of this Loop for that we use the Breck

statement let's trun this program and

see what happens so there you go after

the first attempt you're successful and

there are no more

attempts so once again I want you to pay

great attention to the indentation here

because that's one of the common issues

amongst beginners so here's our for Loop

these two lines are indented with four

spaces and they belong to our for Loop

in every iteration these two lines will

be executed now when we get to line four

if this condition is true then these two

lines will be executed because both

these lines are indented below this if

statement now let's take this program to

the next level what if we attempt three

times and we still cannot send an email

perhaps we want to display a different

message to the user we say hey we Tred

three times but it didn't work so I'm

going to change successful to false now

at the end here we can add an L

statement this is what we call a for l

statement

what we put under this L statement will

only be executed if this Loop completes

without an early termination so if we

never break out of this Loop then the L

statement will be executed so here we

can print a message like attempted three

times and

failed so run the

program see what we get three attempts

followed by this message attempted three

times and failed

in contrast if we change successful to

true because we terminate this Loop

using this break statement what we have

in the else block will not be executed

take a look R the program we have one

attempt successful

done in programming we have this concept

called nested Loops so we can put one

Loop inside of another loop and with

this we can get some interesting results

let me show you so I'm going to start

with this Loop for X in range five colon

now inside of this Loop I'm going to add

another loop so for y in range three

colon and then in our second Loop I'm

going to add a print statement here we

can use formatted strings to display

coordinates remember formatted strings

so we have F followed by quotes now here

we add parentheses for our coordinates

first we want to display X and then

comma followed by y let's run this

program and see what happens there you

go pretty cool isn't it so we get zero

and zero 0o and one zero and two then we

get one and zero one and one one and two

and so on now let me explain how exactly

python interpreter executes this code so

here we have two Loops this is what we

call the outer loop and this is the

inner loop so the execution of our

program starts here in the first

iteration of this Loop X is zero now we

get to this statement which is a child

of this four statement because it's

indented four times this statement

itself is a loop so what we have inside

of this Loop will be executed three

times in the first iteration X is zero

because we're still in the first

iteration of the outer loop and Y is

also zero because we are in the first

iteration of the inner loop that is why

we get zero and zero now we go to the

second iteration of this Inner Loop in

this iteration y will be one whereas X

is still zero that is why we get 0 and

one and similarly in the third iteration

of our inner loop we'll get

zero and two in the terminal now we're

done with the execution of the inner

loop so the control moves back to our

outer loop here will be in the second

iteration so X will be one and then we

start here again so we have to execute

this inner loop three times in the first

iteration y will be zero and X is one so

here we have one and zero then we'll get

one and one and one and two you got the

point so this is all about nested

Loops so you have learned how to use for

Loops to repeat one or more statements

in your programs now let's dive deeper

and see what this range function returns

so earlier you learned about the

built-in type function with this

function we can get the type of an

object so if I pass Five here and run

this program this is what we get so the

type of this number or this object is

int or integer now let's look at the

type of the value that we get from the

range function so as an argument we pass

range of a number let's run this program

so this range function returns an object

of type range so in Python we have

primitive types like numbers strings and

booleans but we also have complex types

range is an example of one of those

complex types throughout this course

you're going to learn about a lot of

other complex types now what is

interesting about this range object is

that it's iterable which means we can

iterate over it or use it in a for Loop

that is why we can write code like

this so This range function returns a

range object which is iterable which

means we can iterate over it in each

iteration X will have a different value

now range objects are not the only

iterable objects in Python strings are

also iterable so here we can add a

string like

python now in each iteration X will hold

one character in this string let me show

you so print X and I'm going to delete

these two lines

here let's run this program so in each

iteration we'll get one character and

print it we have another complex type

called list which we use to store a list

of objects so we add square brackets

this indicates a list now we can add a

list of numbers or a list of strings

like a list of names you will learn

about lists later in the course so let's

run this one more time as you can see we

can iterate over lists in in each

iteration will get one object in this

list now later in the course I will show

you how to create your own custom

objects that are iterable for example

you will learn how to write code like

this for item in shopping cart print

item so shopping cart is going to be a

custom object that you will create it's

not going to be an integer or string or

Boolean it's a custom object it has a

different structure and we'll make it

iterable so we can use it in a for Loop

and in each iteration we can get one

item in the shopping cart and printed on

a

terminal so you have learned that we use

four Loops to iterate over iterable

objects in Python we have another kind

of loop that is a while loop and we use

that to repeat something as long as a

condition is true here's an example so

let's define a variable number and set

it to a 100 now we use while and here we

add a condition as long as number is

greater than zero we add a colon once

again we have indentation so we can

repeat one or more statements we can

print this

number and then we can divide it by half

so number equals

number use the integer division to

divide it by two

or we can use the augmented assignment

operator to shorten this code like

this now let's run this

program so here's what we get initially

our number is 100 we divide it by half

we get 50 then 25 and so on so as you

can see in this example we are not

iterating over an itable like a range

object or a string or a list we are

evaluating a condition and repeating a

task let me show you a real word example

of a y Loop in this interactive shell

python is waiting for an input we can

type something like 2 + 2 it will

evaluate it and ask for the next input

we can add another expression like 10 is

greater than two so these steps will

continue until we press contrl D so

behind the scene we have a y Loop that

continues execution until we press contr

D that is the condition that causes the

Y Loop to terminate let me show you how

to build something like this in

Python so let's Define a variable

command and set it to an empty string

now here we need a y Loop we want this y

Loop to execute as long as command does

not equal to quit so command does not

equal to quit

colon in this Loop we want to continue

continuously get input from the user so

we use the built-in input function we

add a label like this get the result and

store it in the command

variable now at this point python

interactive shell will evaluate this

command we're not going to do that in

this lecture because that's way too

complex for Simplicity we can just Echo

back what the user entered so

print Echo and as the second argument we

as this command so this is our y Loop it

will execute until we type quit now as I

told you before don't run this program

using the code Runner extension because

by default it will run your program in

the output window which is read only so

open up the terminal using control and

back tick and run python or Python 3

app.py so here's our Command Prompt

let's type 2+ two it echoes back let's

type 3 * 2 there you go if we type quit

our program terminates now let's try it

one more time what if we type quit in

uppercase the program doesn't terminate

because as you learned before lowercase

and uppercase characters have different

numeric

representations so quit in lowercase is

different from quit in

uppercase now to solve this problem an

amateur programmer may do something like

this

and command does not equal to Capital

quit so while command does not equal

quit in lowercase and quit in uppercase

continue getting input from the user

let's run this program in terminal and

see what

happens so one more time python

app.py we type quit beautiful it works

we type quit in uppercase that would

work too but what if I type quit with an

uppercase q and lowercase U our program

doesn't terminate so this is a poor way

of checking for the quit command what is

a better way let me show you so we don't

need this end operator here instead

because command is a string we can call

the lower method so whatever the user

types in first will'll convert it to

lowercase and then compare it with quit

in lowercase with this change it doesn't

matter how the user types the word quit

will always terminate the

program now the last thing I want to

discuss in this section is the concept

of infinite Loops an infinite Loop is a

loop that runs forever so if I change

this condition to true because true is

always true this y Loop will will run

forever so to jump out of this we need a

break statement so after we get the

input from the user we can get the

command convert it to

lowercase and see if it equals to quit

if that's the case we want to

break now with this change we no longer

need to initialize command to an empty

string previously we needed this because

we had a while statement like this while

command does not equal will quit so we

had to Define this command variable and

that's why we have set it to an empty

string without this line when python

interpreter tries to execute this code

it doesn't know what command is so now

that we have an infinite Loop we no

longer need to Define command and set it

to an empty string so in terms of

functionality this program is exactly

the same as the program we wrote in the

last lecture just be aware of these

infinite Loops because they run for ever

you should always have a way to jump out

of them otherwise your program will run

forever and this can sometimes cause

issues because if you're executing

operations that consume memory at some

point your program may run out of memory

and

crash all right time for an exercise I

want you to write a program to display

the even numbers between 1 to 10 so when

you run this program you should see 2 4

6 and 8 and after these I want you to

print this message we have four even

numbers now here's a quick hint before

you get started you should call the

range function with one and 10 do not

use the third argument which is called

Step so basically I want you to iterate

over all the numbers between 1 to 10

check if each number is an even number

and then print it on the terminal so

pause the video spend 2 minutes on this

exercise when you're done come back

continue

watching so we start with a for Loop for

number in range 1 to 10

colon we check to see if the remainder

of division of this number by two equal

Z so if number modulus 2 equal Z then

reprint this

number now let's run this

program so we get 2 4 6 8 beautiful now

to count the even numbers we need a

separate variable so let's call that

count initially we set it to zero now in

this if block every time we find an even

number we need to increment count so we

said count plus equals 1 and finally

after our for Loop we can print a

formatted string we have count count

even

numbers let's run the program and here's

the result so that brings us to the end

of this section in the next section

you're going to learn how to create your

own functions I hope you enjoyed the

section and thank you for

watching so far you have learned how to

use some of the built-in functions in

Python such as print round and so on in

this section you're going to learn how

to write your own functions now you

might ask but why do we even need to

write our own functions well when you

build a real program that program is

going to consist hundreds or thousands

of lines of code you shouldn't write all

that code in one file like we have done

so far you should break that code into a

smaller more maintainable and

potentially more reusable chunks you

refer to these chunks as functions so

let me show you how to create your own

custom functions we start with the defa

keyword which is short for Define next

we need to give our function a name so

let's call this greet all the best

practices you learn about naming your

variables also apply to naming your

functions so make sure your function

names are meaningful descriptive use

lowercase letters to name your functions

and an underscore to separate multiple

words now after the name we need to add

parentheses you will see why shortly and

then we'll add a column now what is

going to happen you know it we're going

to get indentation which means the

following statements will belong to this

function so here I'm going to add two

statements hi there and welcome

aboard both these lines belong to this

function because they're

indented now we're done with this

function we need to call it so we remove

the indentation and we add two line

breaks after this function this is what

pep8 recommends to keep our code clean

and maintainable now if you forget to

add two line braks don't worry as soon

as you save the changes autopep8 will

automatically add these line braks for

you let me show you so I'm going to

remove these line braks and call this

function great with parenthesis just

like how we call the built-in functions

now save the changes there you go so we

get two line breaks after our function

now let's run this

program so we get these two messages on

the

terminal now here's a question for you

what is the difference between the GRE

and print functions the difference is

that this print function takes an input

whereas our grd function doesn't take

any inputs so let me show you how to

pass inputs like first name and last

name to this function when defining a

function in between parentheses we list

our parameters so here we add two

parameters like first underline name and

last underline name now when calling

this function we need to supply two

values for those parameters we refer to

them as arguments so m

hamedani these are the arguments to the

greed function that's one of the terms

that a lot of developers out there don't

know they don't know the difference

between parameters and arguments a

parameter is the input that you define

for your function whereas an argument is

the actual value for a given parameter

okay now let's change line two and

instead of saying hi there we can greet

a person by their full name so we can

convert this to a formatted string

and pass two Fields here first name as

well as last name save the changes run

the program and this is what we get in

terminal now this function is more

useful we can reuse it and call it with

different arguments so let's greet John

Smith as well run the program so we get

Hi msh hamadani and hi John Smith now

note that by default all the paramet

that you define for a function are

required so here our greed function

takes two parameters if I exclude one of

these arguments and save the changes you

can see we have this red underline so

pilent is complaining and saying there

is no value for argument last name also

if we run the program we get this type

error greet missing one required

positional

argument so let's put this back now let

ler I will show you how to define

optional

parameters so this is the simplified

version of this great function we

created earlier now in programming we

have two types of functions functions

that perform a task and functions that

calculate and return a value here are

some examples both the print and GD

functions are example of type one

they're performing a task which is

printing something on the terminal in

contrast the round

function is an example of a function

that calculates and returns a value so

the functions that you create fall into

these two categories now let me show you

how to rewrite this great function but

in the second form so instead of

printing this string on the terminal we

simply return it let me show you so I'm

I'm going to delete all this

code Define a new function but call it

get underline greeting we add the name

parameter and simply return this

formatted string High

name that's all we have to do so we use

the return statement to return a value

from this function now we can call this

function get underlined greeting pass a

name like msh because it returns a value

we can store that value in a separate

variable like message now you might be

curious which form of these gting

functions is better well with this first

implementation we loged to printing

something in the terminal in the future

if we want to write that message in a

file or send it in an email we have to

create another function so we cannot

reuse this great function in other

scenarios in contrast this second form

is not tied to printing something on the

terminal it simply returns a value now

we get this value and we can do whatever

we want with it we can print it on the

terminal or we can use the built-in open

function to write this message to a file

so we can create a file like content.

txt open it for writing this returns a

file object and then we can call file.

write message now and don't worry about

these two lines later in the course I'm

going to talk about working with files

but what I want you to take away here is

that we have this message variable and

we can do whatever we want with it we

can print it on the terminal write it to

a file send it in an email and so on and

one more thing before we finish this

lecture so here's our GD function and as

you can see we're simply printing a

string now if we call GRE give it a name

run the program we get this message hi

msh but what if we put this inside of a

call to the print function let's see

what we get we get high M followed by

nonan what is this nonan is the return

value of the great function so in Python

all functions by default return the non

value non is an object that represents

the absence of a value later in the

course you're going to learn more about

nonone what matters now is that all

functions return non by default unless

you specifically return a value so here

if we

return some

string none will no longer be returned

now I just want to clarify something

earlier I told you that we have two

types of functions in programming

functions that carry out a task or

functions that calculate and return a

value so back to the code we previously

had so even though this function returns

nonone by default it is still classified

as a function that carries out a

task let's create another function we

call it increment we want to use this

function to increment a number by a

given value so here we simply return

number plus

by now we can call this function like

this and commment two and one this

returns a value so we can store it in a

variable like result and then print it

on the terminal let's run the program we

get three beautiful now we can simplify

this code we have used this result

variable only in a single place that is

line six so we don't really need it so

on line six we can replace result with a

call to increment function like this

so when python interpreter executes this

code first it will call the increment

function it will get the result and

temporarily store it in a variable for

us we don't see that variable and then

it will pass that variable as an

argument to the print function now if we

run this program we get the exact same

result beautiful now we can make this

code more readable if someone else looks

at line five they may not know exactly

what these arguments are four we can use

a keyword argument to make this code

more readable so this one here is the

value of this by parameter we can prefix

it with the name of the parameter like

this now we can read this code almost

like plain English increment to by one

so if you're calling a function with

multiple arguments and it's not quite

clear what these arguments are for you

can make your code more read

by using keyword arguments so here y

equals 1 is a keyword

argument earlier I told you that all the

parameters that you define for a

function are required by default in this

lecture I'm going to show you how to

make the by parameter optional so let's

say we don't want to

explicitly pass by equals 1 every time

we want to call this incr function we

want to use this function to increment a

value by one so we remove the second

argument now we need to give this

parameter a default value so we set it

to one now if we call this function and

don't Supply the second argument this

default value will be used otherwise the

value that we specify here will be used

let me show you so we run this program

the result is three but if we pass the

second AR argument here will increment

two by five so we will get seven so you

can see it's pretty easy to make a

parameter optional just be aware that

all these optional parameters should

come after the required parameters in

other words I cannot add another

required parameter here let's call that

another I cannot add that here if I save

the changes you can see we get a red

underline here so all the optional

parameters should come after the

required parameters now obviously in

this case we don't need the second

parameter so let's delete

it there are times that you may want to

create a function that takes a variable

number of arguments here is an example

let's define this function multiply that

takes two parameters X and Y and simply

returns x * y now we can call this

function like

this so far so good but what if you want

to pass one or two more arguments here

that doesn't work because our multiply

function takes only two parameters to

solve this problem we need to replace

these two parameters with a single

parameter we use a plural name here to

indicate that this is a collection of

arguments

and then we prefix it with an asterisk

this is the magical part let me show you

what happens when you use an asterisk

here so temporarily let's delete this

line and simply print numbers let's see

what we get here so run the

program you can see all our arguments

and they're packed in parenthesis what

is this well earlier you learned about

lists I briefly mentioned that you can

use square bracket to create a list of

objects like 2 3 4 5 now later in the

course we have a comprehensive section

about lists so don't worry about the

details of lists and how they work but

what I want you to note here is that the

only difference between this list and

what we have here is in the notation so

we use square brackets to create lists

and parentheses to create toles some

people call it tles or tuples so a

topple is similar to a list and that

it's a collection of objects the

difference is that we cannot modify this

collection we cannot add a new object to

this toppo once again later in the

course we're going to have a

comprehensive section about lists top

holes and other data structures what

matters now is that these topples just

like lists are iterable so we can

iterate over them which means we can use

them in Loops let me show you

so let's write for number in numbers

colon let's just print one number at a

time actually we don't need this line so

delete and run the program so we iterate

over this top hole and in each iteration

we get one number and printed on the

terminal so now with a simple change we

can calculate the product of all these

numbers all we have to do is to Define a

variable like total initially we set it

to one and then in each each

iteration we get total and multiply it

by the current number or we can rewrite

this statement using an augmented

assignment operator so total times equal

number line five and four are exactly

identical so I'm going to use LINE five

because it's shorter and cleaner delete

and finally we'll return the total now

one of the issues I see often in

beginnner code is that they don't use

this indentation properly so they put

the return statement here and then they

wonder why their function doesn't work

properly if you put the return statement

here it will be part of the for Loop so

it will be executed in each iteration in

this case after the first iteration

because of this return statement will

return from this multiply function so

the total will not be calculated

properly we need to put this at the same

level of indentation as other statements

in this function so here we have our

four statement we Loop over all the

numbers we calculate the total and then

finally return it so with this

implementation we can get the result and

printed on the terminal let's run the

program and you can see the product of

these numbers is

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