Get aprox number in a list

get_aprox.py

#!/usr/bin/env python
"""
Create a program that given a requested number gives you
the nearest number in a list.

Considerations:
    - The list needs to only contain integers

This example is useful when you have only a certain number of
images sizes available and you have to pick one for your station
collage.

e.g.:
    >>> requested_size = 21
    >>> sizes = (1, 2, 3, 19, 29, 10, 22, 3)
    >>> main(requested_size, sizes)
    22
"""
def minus_one(requested_size, sizes):
    if requested_size in sizes:
        return requested_size
    else:
        requested_size -= 1
        return minus_one(requested_size, sizes)

def plus_one(requested_size, sizes):
    if requested_size in sizes:
        return requested_size
    else:
        requested_size += 1
        return plus_one(requested_size, sizes)
    
def main(requested_size, sizes):
    """
    >>> requested_size = 120
    >>> sizes = (33, 50, 52, 75, 100, 175, 180, 182, 200, 350)
    >>> main(requested_size, sizes)
    100
    """
    if requested_size in sizes:
        return requested_size
    else:
        closest_behind = minus_one(requested_size, sizes)
        closest_ahead = plus_one(requested_size, sizes)
        return closest_ahead if (closest_ahead - requested_size) <= (requested_size - closest_behind) else closest_behind

if __name__ == '__main__':
    import doctest
    doctest.testmod()