Practical Programming, 2nd Edition

Choosing Which Statements to Execute

An if statement lets you change how your program behaves based on a condition. The general form of an if statement is as follows:

if condition:
    block

The condition is an expression, such as color != “neon green” or x < y. (Note that this doesn’t have to be a Boolean expression. As we discussed in ​Using Numbers and Strings with Boolean Operators​, non-Boolean values are treated as True or False when required.)

As with function bodies, the block of statements inside an if must be indented. As a reminder, the standard indentation for Python is four spaces.

If the condition is true, the statements in the block are executed; otherwise, they are not. As with functions, the block of statements must be ...