A Byte of Python

The if statement

We use the if statement to check if a condition is True and if it is True, we run a corresponding set of steps which are specified in a separate block. A block of statements is specified using indentation, that is, using spaces or tabs.

Let us consider an example.

Example 6.1. if statement

#!/usr/bin/env python 
# Filename: if1.py 
 
age = 22 # mention your age here 
 
if age >= 18: # notice the colon
    print 'You are old enough to vote now!' # use tabs or 4 spaces for indentation

Output

$ python if1.py
You are old enough to vote now! 

How It Works

In this example, we are printing a message about whether the user is eligible to vote or not, depending on his/her age. Here, we assume that you need to be 18 years old to vote for an election.

The if statement starts with the if keyword followed by a condition. In this case, the condition is whether the user's age is greater than or equal to 18. The condition is followed by a colon at the end of the line followed by a block of statements.

Notice that the new block of statements is marked using indentation. Indentation means making use of whitespace. Remember that we have already discussed how to use indentation (hint: 4 spaces or tabs).

This new block is also called the if clause since this block is executed only if the condition is True. In our if clause, we have a simple message to indicate that you are legal to vote.

In case, the condition is False, currently our program does not do anything. To indicate that the user will not be able to vote, we can use an else clause:

Example 6.2. if-else statement

#!/usr/bin/env python 
# Filename: if2.py 
 
age = 17 # mention your age here 
 
if age >= 18: # notice the colon
    print 'You are old enough to vote now!' # use tabs or 4 spaces for indentation
else:
    print 'Sorry, you are not old enough to vote'

$ python if2.py
Sorry, you are not old enough to vote

The else clause is part of the if statement and it can have a corresponding block of statements that will be executed if the if condition is False.

if-elif-else clauses

Example 6.3. if-elif-else statement