Boolean

Overview

Python's bool is a subclass of int (True == 1, False == 0). Understanding truthiness (truthy/falsy) is crucial for writing idiomatic Python conditionals and avoiding common bugs.

Syntax

python

# Boolean literals
x = True
y = False

# Falsy values in Python
bool(0)         # False
bool("")        # False
bool([])        # False
bool(None)      # False
bool({})        # False

# Truthy values
bool(1)         # True
bool("hello")   # True
bool([0])       # True  (non-empty list)

Common Pitfalls

True + True == 2 in Python because bool is a subclass of int — avoid arithmetic with booleans.
Use 'is True' vs '== True' carefully — 'if value:' is idiomatic; 'if value == True:' may give unexpected results for non-bool truthy objects.
Interview tip: None, 0, empty collections, and empty strings are all falsy — useful for default/guard patterns.

Real-World Example

Using truthiness to guard against empty inputs

example

python

def process(data: list) -> str:
    if not data:                    # same as: if len(data) == 0
        return "No data provided"
    return f"Processing {len(data)} items"

print(process([]))        # "No data provided"
print(process([1, 2, 3])) # "Processing 3 items"

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