Variables, Expressions, Conditions and Functions

 Making a Python file: 

Python files are stored with the extension “.py”. Open a text editor and save a file with the name “hello.py”. Open it and write the following code:

• Python3

print ("Hello World") # Notice that NO semi-colon is to be used

Reading the file contents: 
Linux System – Move to the directory from the terminal where the created file (hello.py) is stored by using the ‘cd’ command and then type the following in the terminal : 

python hello.py

Windows system – Open command prompt and move to the directory where the file is stored by using the ‘cd’ command and then run the file by writing the file name as a command.

Variables in Python 
Variables need not be declared first in python. They can be used directly. Variables in python are case-sensitive as most of the other programming languages. 

Example: 

• Python3

a = 3 A = 4 print (a) print (A)

The output is : 

3
4

Time Complexity: O(1)

Auxiliary Space: O(1)

Expressions in Python 
Arithmetic operations in python can be performed by using arithmetic operators and some of the in-built functions. 

• Python3

a = 2 b = 3 c = a + b print (c) d = a * b print (d)

The output is : 

5
6

Time Complexity: O(1)

Auxiliary Space: O(1)

Conditions in Python 
Conditional output in python can be obtained by using if-else and elif (else if) statements. 

• Python3

a = 3 b = 9 if b % a == 0 :     print ("b is divisible by a") elif b + 1 == 10:     print ("Increment in b produces 10") else:     print ("You are in else statement")

The output is : 

b is divisible by a

Time Complexity: O(1)

Auxiliary Space: O(1)

Functions in Python 
A function in python is declared by the keyword ‘def’ before the name of the function. The return type of the function need not be specified explicitly in python. The function can be invoked by writing the function name followed by the parameter list in the brackets. 

• Python3

# Function for checking the divisibility # Notice the indentation after function declaration # and if and else statements def checkDivisibility(a, b):     if a % b == 0 :         print ("a is divisible by b")     else:         print ("a is not divisible by b") #Driver program to test the above function checkDivisibility(4, 2)

The output is : 

a is divisible by b

Time Complexity: O(1)

Auxiliary Space: O(1)

So, python is a very simplified and less cumbersome language to code in. This easiness of python is itself promoting its wide use.