3.5. Truth Value

By definition, truth value of X is the True/False value returned when bool(X) is performed.

In general, if any value has some content, it has a truth value of True. If a value does not have any content, its truth value is False.

Truth value for `str` type

A string has a truth value of True when it is non-empty.

CodeOutput

print(bool(''))
print(bool('a'))

False
True

In first line, an empty string has truth value of False and in second line, a non-empty string has truth value of True.

Note that a space is also considered a character so truth value of " " is also True.

CodeOutput

print(bool(' '))

True

Even if string has no actual characters, a "space" is still considered a character so string is not empty and has truth value of True.

An integer has a truth value of True when it is non-zero.

CodeOutput

print(bool(0))
print(bool(1))
print(bool(2))

False
True
True

A floating point number has a truth value of True when it is non-zero.

CodeOutput

print(bool(0.0))
print(bool(1.2))

False
True

Note that the value has to be absolutely 0.0 to be False. A value as small as 0.00000001 also has some content so its truth value is True.

CodeOutput

print(bool(0.0))
print(bool(0.000000001))

False
True

Truth values are used in if/elif statements. They are a shorthand to checking if the content of variable being checked is non-empty.

OutputCode

content = ''

if content:
    print('Non-empty')
else:
    print('Empty')

Empty

Here, the if statement checks if the value of content is non-empty. This is roughly equivalent to:

content = ''

if content != '':
    print('Non-empty')
else:
    print('Empty')

Same goes for integers and floats. If an integer is non-zero, only then it would evaluate to True in an if statement.