Valid quantity?

A customer can order between 1 and 20 of an item. Write is_valid_quantity(q) that returns True if q is in that range, inclusive, and False otherwise.

is_valid_quantity(1)   ->  True
is_valid_quantity(20)  ->  True
is_valid_quantity(0)   ->  False
is_valid_quantity(21)  ->  False

def is_valid_quantity(q):
    ...