note.nkmk.me

Convert Between bool (True/False) and Other Types in Python

Modified: | Tags: Python

In Python, Boolean values (truth values) are represented by the bool type objects True and False. This article explains how to convert between bool and other types in Python.

Contents

bool is a Subclass of int

Both True and False are instances of the bool type:

print(type(True))
# <class 'bool'>

print(type(False))
# <class 'bool'>
source: bool_example.py

Moreover, bool is a subclass of int:

print(issubclass(bool, int))
# True
source: bool_example.py

True and False Are Equivalent to 1 and 0

In Python, True is equivalent to 1 and False is equivalent to 0:

print(True == 1)
# True

print(False == 0)
# True
source: bool_example.py

Because bool is a subclass of int, Boolean values can be used in arithmetic operations:

print(True + True)
# 2

print(True * 10)
# 10
source: bool_example.py

This means you can count the number of True values in a list using the built-in sum() function:

print(sum([True, False, True]))
# 2
source: bool_example.py

You can also use a generator expression to count the number of elements that meet a condition. A generator expression is similar to a list comprehension, but uses parentheses () instead of square brackets [].

If the generator expression is the only argument to a function, you can omit the parentheses:

l = [0, 1, 2, 3, 4]

print([i > 2 for i in l])
# [False, False, False, True, True]

print(sum(i > 2 for i in l))
# 2
source: bool_example.py

Truth Value Testing in Python

In Python, objects other than True and False can also evaluate as either true or false in conditionals such as if statements.

The following are considered falsy:

All other objects are considered truthy. For example, a non-empty string is truthy:

if 'abc':
    print('True!')
# True!
source: bool_example.py

Convert Other Types to bool: bool()

bool() evaluates an object according to Python’s rules for truth value testing and returns either True or False.

Any non-empty string, including 'True' and 'False', is treated as True. Only an empty string becomes False. To convert a string based on its content, use strtobool() (explained below):

print(bool('True'))
print(bool('False'))
print(bool('abc'))
# True
# True
# True

print(bool(''))
# False
source: bool_test.py

Non-zero numbers evaluate to True; zero values evaluate to False:

print(bool(1))
print(bool(2))
print(bool(1.23))
print(bool(-1))
# True
# True
# True
# True

print(bool(0))
print(bool(0.0))
print(bool(0j))
# False
# False
# False
source: bool_test.py

Non-empty sequences and collections are True; empty ones are False:

print(bool([1, 2, 3]))
print(bool((1, 2, 3)))
print(bool({1, 2, 3}))
print(bool({'k1': 1, 'k2':2, 'k3': 3}))
# True
# True
# True
# True

print(bool([]))
print(bool(()))
print(bool({}))
# False
# False
# False
source: bool_test.py

The special constant None is always evaluated as False.

print(bool(None))
# False
source: bool_test.py

Convert Strings to bool Based on Content: strtobool()

As mentioned above, bool('False') still returns True because it's a non-empty string. To convert strings based on their content, use strtobool().

Up to Python 3.11, strtobool() was included in the standard library's distutils.util module. In Python 3.12 and later, since distutils has been removed, it is available via the setuptools package, which is not part of the standard library and must be installed separately (e.g., using pip).

# For Python 3.11 and earlier
from distutils.util import strtobool

# For Python 3.12 and later (requires installing setuptools)
from setuptools._distutils.util import strtobool

The following case-insensitive strings are considered valid inputs:

  • Truthy: 'y', 'yes', 't', 'true', 'on', '1'
  • Falsy: 'n', 'no', 'f', 'false', 'off', '0'

Any other input will result in a ValueError.

True values are y, yes, t, true, on and 1; false values are n, no, f, false, off and 0. Raises ValueError if val is anything else. 9. API Reference - distutils.util.strtobool(val) — Python 3.11.12 documentation

Previously, strtobool() returned 1 or 0 (as integers), but starting with setuptools version 75.3.2 (released on 2025-03-12), it returns True or False.

from setuptools._distutils.util import strtobool

print(strtobool('true'))
print(strtobool('True'))
print(strtobool('TRUE'))
# True
# True
# True

print(strtobool('t'))
print(strtobool('yes'))
print(strtobool('y'))
print(strtobool('on'))
print(strtobool('1'))
# True
# True
# True
# True
# True

print(strtobool('false'))
print(strtobool('False'))
print(strtobool('FALSE'))
# False
# False
# False

print(strtobool('f'))
print(strtobool('no'))
print(strtobool('n'))
print(strtobool('off'))
print(strtobool('0'))
# False
# False
# False
# False
# False
source: setuptools_strtobool.py

Invalid inputs raise a ValueError:

# print(strtobool('abc'))
# ValueError: invalid truth value 'abc'
source: setuptools_strtobool.py

To support non-standard inputs, use a try-except block:

try:
    strtobool('abc')
except ValueError as e:
    print(e)
# invalid truth value 'abc'
source: setuptools_strtobool.py

If you want to support additional input strings, you can define your own version of strtobool() based on the implementation in setuptools.

def strtobool(val: str) -> bool:
    """Convert a string representation of truth to true (1) or false (0).

    True values are 'y', 'yes', 't', 'true', 'on', and '1'; false values
    are 'n', 'no', 'f', 'false', 'off', and '0'.  Raises ValueError if
    'val' is anything else.
    """
    val = val.lower()
    if val in ('y', 'yes', 't', 'true', 'on', '1'):
        return True
    elif val in ('n', 'no', 'f', 'false', 'off', '0'):
        return False
    else:
        raise ValueError(f"invalid truth value {val!r}")
source: util.py

It uses lower() to normalize case and checks membership using the in operator.

Convert bool to Other Types

To numbers: int(), float(), complex()

Since True and False are equivalent to 1 and 0, they can be converted to numeric types:

print(int(True))
print(int(False))
# 1
# 0

print(float(True))
print(float(False))
# 1.0
# 0.0

print(complex(True))
print(complex(False))
# (1+0j)
# 0j
source: bool_example.py

To String: str()

Use str() to convert True and False to the strings 'True' and 'False':

print(str(True))
print(str(False))
# True
# False

print(type(str(True)))
print(type(str(False)))
# <class 'str'>
# <class 'str'>
source: bool_example.py

Keep in mind that all non-empty strings are truthy, so converting False to a string and back to bool results in True:

print(bool(str(False)))
# True
source: bool_example.py

To Other Types

You cannot directly convert True or False into a list or tuple. Doing so raises a TypeError because bool objects are not iterable:

# print(list(True))
# TypeError: 'bool' object is not iterable
source: bool_example.py

Related Categories

Related Articles