19.4: Boolean Functions

Functions can return booleans, which is often convenient for hiding complicated tests inside functions. For example:

def is_divisible(x, y):
    if x % y == 0:
        return True
    else:
        return False

It is common to give boolean functions names that sound like yes/no questions; is_divisible returns either True or False to indicate whether x is divisible by y.

Here is an example:

>>>   is_divisible(6, 4)
False
>>>   is_divisible(6, 3)
True

The result of the == operator is a boolean, so we can write the function more concisely by returning it directly:

def is_divisible(x, y):
    return x % y == 0

Boolean functions are often used in conditional statements:

if is_divisible(x, y):
    print 'x is divisible by y'

It might be tempting to write something like:

if is_divisible(x, y) == True:
    print 'x is divisible by y'

But the extra comparison is unnecessary.

Exercise \(\PageIndex{1}\)

Write a function is_between(x, y, z) that returns True if x ≤ y ≤ z or False otherwise