The Boolean Type in Python

Today we’ll be talking about the boolean type in Python.

The boolean data type can have only one of two values: True or False.

We can assign a boolean value explicitly:

>>> she_is_coming = True
>>> if she_is_coming == True:
...     print("Beware...")
... 
Beware...

>>> winning = False
>>> if winning == False:
...     print("Try harder!")
... 
Try harder!

We can rewrite this code in a more concise manner. In the condition check we can write just she_is_coming, which is equivalent to she_is_coming == True:

>>> if she_is_coming:
...     print("Beware...")

Accordingly, the equivalent of winning == False is not winning:

>>> if not winning:
...     print("Try harder!")

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Expressions can evaluate to a boolean value. They can be practically of any length and complexity:

>>> 2 + 3 == 8
False

>>> 3 > -11
True

>>> len("Hi there") < 100
True

>>> ["I", "you", "she", "they"][1] == "they"
False

>>> max([5, 16, 2]) <= len("just counting") + min((7, 0, -3, 8))
False

We can check whether an expression is of boolean type using the type function:

>>> type(2 + 2 == 4)
<class 'bool'>

The boolean values True and False may even be used as numbers. Then True equals 1 and False equals 0:

>>> 2 * True
2

>>> False + 8 - True
7

In such a case the boolean value doesn’t change the numeric type of the expression:

>>> a = False + 3
>>> type(a)
<class 'int'>

>>> b = 3.75 * True
>>> type(b)
<class 'float'>

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Numbers may also be understood as boolean values. Zero is understood as False, any other number as True.

So, here we have a condition which is not met:

>>> if 0:             # means as much as ‘if False’
...     print(3)
... 

The following two conditions are met:

>>> if 54:            # means as much as ‘if True’
...     print(5)
... 
5

>>> if -56:           # means as much as ‘if True’
...     print("hi")
... 
hi

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Actually, there are a few objects which are evaluated as False:

– the boolean literal False

– numerical 0 values (integer 0, float 0.0, complex 0.0+0.0j)

– empty strings, lists, tuples and dictionaries

– the value None

Other objects are evaluated as True.

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