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How to Use Booleans in If Statements in Python

Booleans (True and False) are essential for controlling program flow.

This guide explores how to effectively use booleans in if statements in Python, covering checks for explicit boolean values, truthiness, falsiness, and combining conditions with logical operators.

Checking for Boolean Values with is​

The is operator is used to check if a variable has a specific boolean value (True or False).

Checking for True​

To check if a variable is True, use the is operator:

variable = True
if variable is True:
    print('The boolean is True')  # Output: The boolean is True
  • The is operator compares object identities and is the recommended way to check for True, False and None.

Checking for False​

To check if a variable is False, use is False or use the not operator:

variable = False
if variable is False:
    print('The boolean is False') # Output: The boolean is False

if not variable:
    print('The variable stores a falsy value') # Output: The variable stores a falsy value
note

Always use the is operator when comparing with boolean constants True and False, and when checking if a variable is None. Do not use equality comparisons like variable == True, which are less specific.

Checking for Truthy and Falsy Values​

You can also use a boolean in an if statement to implicitly check for its truthiness or falsiness:

variable = True
if variable:
    print('The variable stores a truthy value') # Output: The variable stores a truthy value
  • Python defines certain values as "truthy" and others as "falsy."
  • If a variable is truthy, the if block runs.

The following values are considered falsy:

  • None and False
  • Numerical zero (0, 0.0, 0j, etc.).
  • Empty sequences and collections: '', (), [], {}, set(), range(0).

All other values are considered truthy:

if 'hello':
    print('this runs ✅') # Output: this runs ✅

if ['a', 'b']:
    print('This runs ✅') # Output: This runs ✅

if '':
    print('this does NOT run ⛔️') # This does NOT run

if 0:
    print('this does NOT run ⛔️') # This does NOT run
  • The if '' statement does not run, as an empty string is considered falsy.
  • The if 0 statement does not run, as numerical zero is considered falsy.

To check for a falsy value you can use the not operator:

variable = False
if not variable:
    print('The variable stores a falsy value') # Output: The variable stores a falsy value

Combining Conditions with and and or​

You can combine boolean expressions using the and and or operators.

  • and: Both conditions must be true for the if block to run.

    if True and True:
        print('This runs ✅') # Output: This runs ✅
    if True and False:
        print('This does NOT run ⛔️') # This does NOT run

  • or: At least one condition must be true for the if block to run.

    if True or False:
        print('This runs ✅') # Output: This runs ✅

    if False or False:
        print('This does NOT run ⛔️') # This does NOT run

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