Python If...Else

Python Conditions and If statements

Python supports the usual logical conditions from mathematics:

• Equals: a == b
• Not Equals: a != b
• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b

These conditions can be used in several ways, most commonly in "if statements" and loops.

An "if statement" is written by using the if keyword.

In this example we use two variables, a and b, which are used as part of the if statement to test whether b is greater than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we print to screen that "b is greater than a".

How If Statements Work

The if statement evaluates a condition (an expression that results in True or False). If the condition is true, the code block inside the if statement is executed. If the condition is false, the code block is skipped.

Indentation

Python relies on indentation (whitespace at the beginning of a line) to define scope in the code. Other programming languages often use curly-brackets for this purpose.

Multiple Statements in If Block

You can have multiple statements inside an if block. All statements must be indented at the same level.

Using Variables in Conditions

Boolean variables can be used directly in if statements without comparison operators.

Python can evaluate many types of values as True or False in an if statement.

Zero (0), empty strings (""), None, and empty collections are treated as False. Everything else is treated as True.

This includes positive numbers (5), negative numbers (-3), and any non-empty string (even "False" is treated as True because it's a non-empty string).