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Python bool() Function

How the Python bool() function converts values to True or False, including falsy values like 0, None, empty sequences, and truthy values like numbers, strings, and non-empty collections.

The bool() function converts a value to a boolean value i.e. one of True or False.

If the value is not specified, the method returns False.

Syntax

bool(value)

bool() Parameters

Python bool() function parameters:

Parameter Condition Description
value Optional Any object (like Number, List, String etc.), Any expression (like x > y, x in y).

bool() Return Value

Python bool() function returns:

  • False: if argument is empty, False, 0 or None
  • True: if argument is any number (besides 0), True or a String

Falsy Values in Python

Falsy values are those that evaluate to False in a boolean context:

  • Constants defined to be false: None and False.
  • Zero of any numeric type: Integer (0), Float (0.0), Complex (0j), Decimal(0), Fraction(0, 1).
  • Empty sequences and collections: Lists ([]), Tuples (()), Dictionaries ({}), Sets (set()), Strings (""), range(0)
  • Any custom object for which the __bool__() method is defined to return False, or the __len__() method returns 0 when __bool__() is not defined.

Examples

Examples of bool() function on falsy values:

print(bool(0))			# Output False
print(bool([]))			# Output False
print(bool(0.0))		# Output False
print(bool(None))		# Output False
print(bool(0j))			# Output False
print(bool(range(0)))	# Output False

Examples of bool() function on truthy values:

print(bool(1))			# Output True
print(bool([0]))		# Output True
print(bool([1, 2, 3]))	# Output True
print(bool(10))			# Output True
print(bool(3+4j))		# Output True
print(bool(range(2)))	# Output True
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