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Python Boolean

Python Booleans are used to represent the truth value of an expression.

The Python Boolean type has only two possible values: True and False.

note

Note that the boolean values True and False begin with the capital letters T and F.

Create Python Boolean​

It is sufficient to assign to a variable a value or an expression that returns a boolean value.

my_boolean = True
is_ok = False
note

In general, a boolean value is obtained as the result of comparison operators or from functions that return booleans.

See paragraphs below.

Boolean Operation​

And Operation​

The operator and returns True if all operands are True, otherwise False.

print(True and True)   # True
print(True and False)  # False
print(False and True)  # False
print(False and False) # False

Or Operation​

The or operator returns True if at least one of the elements is True, otherwise False.

print(True or True)   # True
print(True or False)  # True
print(False or True)  # True
print(False or False) # False

Not Operation​

The not operator returns the inverse value to the input value.

print(not True)  # False
print(not False) # True

Comparison Operators​

Comparison operators always return Boolean values.

Equality and Inequality​

The most common comparison operators are the **equality operator == and the inequality operator !=.

print(1 == 1)   # True
print(1 == 1.0) # True
print(1 == 2)   # False
print(1 != 2)   # True
print(1 != 1)   # False

Order Comparisons​

Order comparison operators are < , <=, > and >=.

print(1 <= 1)
print(1 < 1)
print(2 > 3)
print(2 >= 2)

In addition, type comparisons are not supported

print(1 <= "1")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '<=' not supported between instances of 'int' and 'str'
note

Order comparison operators are not defined for all objects (also because some objects have no meaningful order like dictionaries).

warning

Python does not require comparison operators to return booleans. Third-party libraries may return different values.

Chaining Comparison Operator​

is Operator​

The is operator checks for objects identity, i.e., x is y evaluates True only when x and y evaluate the same object.

x = []
y = []
print(x is x)     # True
print(x is not x) # False
print(x is y)     # False
print(x is not y) # True
note

The examples above show the is operator used only with lists. The behavior of the is operator on immutable objects such as numbers and strings is more complicated.

in Operator​

The in operator checks for membership.

note

An object can define what it considers to be members.

Most sequences, such as lists, consider their elements to be members.

For example:

my_list = [2, 4, 6, 8, 10]
print(1 in my_list)      # False
print(2 in my_list)      # True
print(10 in my_list)     # True
print(10 not in my_list) # False

Conversion other datatypes in Boolean​

The bool() function​

The bool() function returns the boolean value of a specified object.

print(bool('Hi')) # True
print(bool(100))  # True
print(bool(0))    # False
print(bool(1))    # True

print(bool(''))  # False
print(bool(()))  # False
print(bool([]))  # False
print(bool({}))  # False
note

The bool() function will always return True, unless:

  • The object is empty, like [], (), {}, ''
  • The object is False
  • The object is 0
  • The object is None

Numbers as Boolean Values​

For numbers, bool(x) is equivalent to x != 0.

This means that it returns False only with 0.

 print(bool(3))
 print(bool(-5))
 print(bool(0))
note

All nonzero integers are true. This also applies to floating-point numbers, including special floating-point numbers such as infinity and Not a Number (NaN).

Other command numbers datatype:

  • fractions (from the fractions module) are False only when they are equal to 0.
  • decimal (from the decimal module) are False only when they are equal to 0.

Sequences as Boolean Values​

In general, objects that have a len() are False when the result of len() is 0 (no matter whether they are lists, tuples, sets, strings, or byte strings)

print(bool([1])) # True
print(bool([]))  # False

print(bool((1,2))) # True
print(bool(()))    # False

print(bool({1,2,3})) # True
print(bool(set())))  # False

print(bool({1: 2}))  # True
print(bool({}))      # False

print(bool("TutRef")) # True
print(bool(""))       # False

print(bool(b"xyz")) # True
print(bool(b""))    # False
note

All Python built-in objects that have a length follow this rule.

So this rule is not guaranteed to work for non-built-in objects!

None as a Boolean Value​

None is always evaluated as False.

print(bool(None)) # False
note

It is best to explicitly verify the identity with is None.

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