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Introduction to Python Programming - Part - I

Instructor: Dr. Sanasam Ranbir Singh

This tutorial is prepared by Mr. Soumyadeep Jana, OSINT Lab, Dept. of CSE, IIT Guwahati

Introduction

  1. Python is a widely-used general-purpose, high-level programming language. It was initially designed by Guido van Rossum in 1991 and developed by Python Software Foundation
  2. Syntax is much simpler to other mid-level languages like C/C++
  3. It is an interpreted language
  4. Widely used today in fields like Machine Learning and AI due to its simplicity and powerful packages developed by the community

1.Installing Python [Version- 3.10]

Windows : Install python and pip

Linux :Install Python

 Install Pip

a) pip is a python package manager that lets you install powerful python packages developed by open-source developers.

b) For windows, pip is installed when you install python.

For linux users, you need to install it seperately

c) pip install 'package_name'

d) More on pip


Install a code-editor, Sublime Text or VS-code to write your python scripts

###2.Print Statement

Used to display output in the terminal

In [ ]:
print('Welcome to Python Programming Lab')
print('India stands 4th at the Commonwealth Games 2022')

#Multiple items with print
print('MTech','Data','Science')
Welcome to Python Programming Lab
India stands 4th at the Commonwealth Games 2022
MTech Data Science
In [ ]:
#WARNING[Python 2 and earlier]
print 'Python Programming'

3.Data Types

data_types.jpg

(3.1) Numeric Types

In [ ]:
#Integer
num1 = 100
print(type(num1))

#Float
num2 = 100.1
print(type(num2))
<class 'int'>
<class 'float'>

Note : No Concept of short, long, double or other modifiers as in C/C++/Java

(3.2) Boolean Types

In [ ]:
var1 = True
print(type(var1))

var2 = False
print(type(var2))
<class 'bool'>
<class 'bool'>

(3.3) String type


1. Represents sequence of characters


2. Enclosed within quotes(either single or double)


3. If you want a string literal to contain either a single-quote or an apostrophe as part of the

string, you can enclose the string literal in double-quote marks

In [ ]:
x = 'IITG ranks 7th in NIRF Engineering category'
print(x)

y = "IITG ranks 7th in NIRF Engineering category"
print(y)

z = "It's raining cats and dogs"
print(z)
IITG ranks 7th in NIRF Engineering category
IITG ranks 7th in NIRF Engineering category
It's raining cats and dogs

NOTE :Unlike C/C++/Java there's no char type here, even a single character is treated as a string

4.Variables

A variable is a name that represents a value stored in the computer’s

memory.

4.1) You use an assignment statement to create a variable and make it reference a piece of data.

An assignment statement is written in the following general format:

variable = expression


Example:

In [ ]:
dollars = 2.75
print(dollars)

#Reassign variable
dollars = 99.95
print(dollars)
2.75
99.95

var_reassign.PNG

WARNING! You cannot use a variable until you have assigned a value to it. An error

will occur if you try to perform an operation on a variable, such as printing it, before

it has been assigned a value.

In [ ]:
temperature = 40
print(temp)
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-7-28ce6b64cc4d> in <module>
      1 temperature = 40
----> 2 print(temp)

NameError: name 'temp' is not defined

(4.2) Variable Naming Conventions

In [ ]:
1age = 3
print(1age)
  File "<ipython-input-8-844bd70ed252>", line 1
    1age = 3
       ^
SyntaxError: invalid syntax

(4.3) Python is a loosely typed language - You don't have to declare variables with data types unlike JAVA or C or C++ etc


What a relief !!!

In [ ]:
int a = 10
float b  100.1
In [ ]:
name = "Lakshya Sen"
age = 20
medal = "gold"
print(name,age,medal)
Lakshya Sen 20 gold
In [ ]:
#Benefit of loose type - single variable can hold multiple datatypes
dollars = "Virat Kohli"
print(x)
x = 7
print(x)
IITG ranks 7th in NIRF Engineering category
7

###5.Reading Input

1.Most of the programs that you will write will need to read input and then perform an operation on that input


2. input() function is used to do this


3. General Format : var = input("Input Message")

(5.1) Reading string type data from keyboard

In [ ]:
x = input("Enter your name")
print(x)
Enter your namesoumyadeep
soumyadeep

Note: input() function returns any input as string

In [ ]:
x = input("Enter your age")
print(x)
print(type(x))
Enter your age25
25
<class 'str'>

(5.2) Reading numeric data types

In [ ]:
#Read integer type data
x = int(input("Enter your age"))
print(x)
print(type(x))

#Read float type data
y = float(input('Enter your cgpa'))
print(y)
print(type(y))
Enter your age25
25
<class 'int'>
Enter your cgpa8.9
8.9
<class 'float'>

###6.Output Formatting

(6.1) Print variables with strings

In [ ]:
wickets = int(input("Enter wickets"))

print("Hopefully India doesn't lose by {} wickets remaining this time against Pak".format(wickets))

print(f"Hopefully India doesn't lose by {wickets} wickets remaining this time against Pak")
Enter wickets10
Hopefully India doesn't lose by 10 wickets remaining this time against Pak
Hopefully India doesn't lose by 10 wickets remaining this time against Pak

(6.2) Suppressing the print Function’s Ending Newline


The print function normally displays a line of output. For example, the following three

statements will produce three lines of output:

In [ ]:
print('One')
print('Two')
print('Three')
One
Two
Three
In [ ]:
print('One', end=" ")
print('Two', end=' ')
print('Three')
One Two Three
In [ ]:
print('One', end=',')
print('Two', end=',')
print('Three')
One,Two,Three

(6.3) Formatting Numbers


format(variable,specifier) function is used to do this

In [ ]:
x = 5000/12
print(x)
416.6666666666667
In [ ]:
x = 5000/12
print(format(x,'.2f'))
print(format(x,'.1f'))
416.67
416.7
In [ ]:
print(format(123456, ',d'))
123,456

Read more about formatting here

7.Conditional Statements

(7.1) If-Else Statement

if-else.PNG

```

if condition:

statement

statement

etc.

else:

statement

statement

etc.

```

In [ ]:
temperature = 36

if temperature < 40:
  print("A little cold,isn't it?")
  print("Turn up the heat!!")
else:
  print("Nice weather we're having")
  print("Pass the sunscreen")
A little cold,isn't it?
Turn up the heat!!

Note : Indentation is extremely important! Use TAB instead of Space

INDENTATION HELL !!!

In [ ]:
number = 5

if number == 1:
 print('One')
else:
  if number == 2:
    print('Two')
  else:
    if number == 3:
      print('Three')
    else:
      print('Unknown')

(7.2) If-Elif-Else Statement


When multiple conditions need to be tested

```

if condition_1:

statement

statement

etc.

elif condition_2:

statement

statement

etc.

else:

statement

statement

etc.

```

Need For If-Elif-Else

In [ ]:
number = 5
if number == 1:
  print("one")
elif number == 2:
  print("two")
elif number == 3:
  print("three")
else:
  print("unknown")

(7.3) Relational Operators and Boolean Expressions

relational_operators.png

Read about how strings are compared here

(7.4) Logical Operators


Logical Operators.png

In [ ]:
a=34
b=26
if a>1 or b>1:
  print("something")
something

Short-Circuit Evaluation of Logical Operators


1) In case of and operator, if the left boolean expression evaluates to False, then the entire compound boolean expression evaluated to FALSE without the right boolean expression being checked


2) In case of or operator, if the left boolean expression evaluates to True, then the entire compound boolean expression evaluated to True without the right boolean expression being checked

In [ ]:
#Short-circuiting of and operator

num = 10
if num>10 and num%2 == 0:
  print("Ok")
else:
  print("Not OK")
Not OK
In [ ]:
#Short-circuiting of or operator

num = 10
if num==10 or num%2 == 0:
  print("Ok")
else:
  print("Not OK")
Ok

8.Let's recapitulate what we have learnt so far with this question

Determine whether a customer qualifies for a loan based on the following criteria


(a)Annual salary is greater than 300000


(b)Minimum work Experience is greater than 3 years

9.Some More Operators with their precedence and associativity

Read here

10.Repetition Structures - Loops

(10.1)Motivation

In [ ]:
a = 10
print(a)
print(a+1)
print(a+2)
print(a+3)
print(a+4)
#.
#.
#.
print(a+100)

mahobila.gif

We can do better!!

In [ ]:
a = 10
for i in range(100):
  print(a+i)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
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success-great-job.gif

Notion of Repetition Structures


while.PNG

(10.2) While Loop


1.Condition Controlled Loop


2.Executes the statements inside until the given condition is TRUE

In [ ]:
#Initialize a starting condition
life = 10

#Declare the loop
while life > 0:
  print(f'Lives Remaining {life}')
  life = life - 1
Lives Remaining 10
Lives Remaining 9
Lives Remaining 8
Lives Remaining 7
Lives Remaining 6
Lives Remaining 5
Lives Remaining 4
Lives Remaining 3
Lives Remaining 2
Lives Remaining 1

BEWARE OF INFINITE LOOPS


rainbow-skull.gif

In [ ]:
#Initialize a starting condition
life = 10

#Declare the loop
while life > 0:
  print(f'Lives Remaining {life}')
In [ ]:
#Another way to represent infinite loop

while True:
  print('DEAD!!')

(10.3) For Loop


1.Count Controlled Loop


2.Used when the no of times the loop needs to execute is known beforehand

In [ ]:
#Execute loop for 5 times
for num in [1,2,3,4,5]:
  print(num)
1
2
3
4
5

for.PNG

In [ ]:
#Use Range function instead of manually typing out the numbers
for num in range(10,0,-1):
  print(num)
10
9
8
7
6
5
4
3
2
1
In [ ]: