Find a median in a Pyton list of integers or floats

find_median.py

def median(xs):
    """
    When given a standard Python list of numbers, this function will
    return the median value. There are a few cases to consider:

    1. xs is an empty list: return None

    2. A list with one element: returns that element

    3. A list with an odd number of elements: Returns the middle value.

    4. A list with an even count of elements: Returns the mean of
    two points in the middle.

    This function is ALLOWED to mutate the list during sorting. It doesn't
    need to make a copy first.

    Parameters
    ----------
    xs: A standard Python list of float or integer values.

    Returns
    -------
    The median as described above
    """
    if len(xs) == 0:
        return None
    elif len(xs) == 1:
        return xs[0]
    elif len(xs) % 2 == 1:
        xs.sort()
        middle_idx = len(xs) // 2
        return xs[middle_idx]
    else:
        xs.sort()
        a_idx = len(xs) // 2
        b_idx = len(xs) // 2 - 1
        return (xs[a_idx] + xs[b_idx]) / 2


if __name__ == '__main__':
    print(median([]))
    print(median([1]))
    print(median([2, 1, 3]))
    print(median([2, 1, 7, 7, 7, 3, 3]))