22.7: Returning True or False

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It’s common for a programmer to want a function which, instead of returning a number or text, tells her whether or not something is true. This lets her use the return value of such a function as the condition of an if statement.

Here’s a trivial example:

Code \(\PageIndex{1}\) (Python):

def is_old_enough_to_vote(age):

if number >= 18:

return True

else:

return False

x = is_old_enough_to_vote(13)

if x:

print("Yes, a 13-year-old can vote!")

else:

print("Alas, a 13-year-old must wait.")

if is_old_enough_to_vote(19):

print("Yes, a 19-year-old can vote!")

else:

print("Alas, a 19-year-old must wait.")

| Alas, a 13-year-old must wait.

| Yes, a 19-year-old can vote!

The values True and False are called boolean values, after the 19th-century mathematician George Boole. Note that in Python they must begin with capital letters.

The somewhat odd-looking “if x:” line is possible because x was set to the return value of a call to is_old_enough_to_vote(), and that function returned a boolean value.