Self implemented strip funciton compared to built-in

strip.py

from string import whitespace
import timeit


def strip(string, chars=whitespace):
    if not isinstance(string, (str, bytes)) \
            or not isinstance(chars, type(string)):
        raise ValueError
    left = 0
    for left, s in enumerate(string):
        if s not in chars:
            break
    right = 0
    for right, s in enumerate(reversed(string)):
        if s not in chars:
            break

    return string[left:len(string) - right]


def test():
    print('self', timeit.timeit(r"strip('\t\nabc  ')", globals=globals()))
    print('builtin', timeit.timeit(r"'\t\nabc  '.strip()"))


if __name__ == '__main__':
    test()