# 6.4: Boolean functions

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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.

As an exercise, write a function is_between(x, y, z) that returns True if $$x \leq y \leq z$$ or False otherwise.

This page titled 6.4: Boolean functions is shared under a CC BY-NC 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .