r/learnpython 23-01-2018

script.py

def none_slice_gabriel(lst, start, stop):
    i = start

    while i < 0 and i < stop:
        yield None
        i += 1

    while i < len(lst) and i < stop:
        yield lst[i]
        i += 1

    while i < stop:
        yield None
        i += 1

def none_slice_elbiot(mylist, start, stop):
    length = len(mylist)
    if stop < start:
        raise ValueError('{} is not less than {}'.format(start, stop))
    elif (stop < 0) or (start > length-1):
        return [None] * (stop - start)
    else:
        part1 = [None] * (0 - min(start, 0))
        part2 = mylist[max(start, 0):stop]  # negative start causes empty
        part3 = [None] * max(0, stop-length)
        return part1 + part2 + part3

def main():
    test_cases = [
        (-5, -5, []),
        (-5, 0, [None] * 5),
        (-2, 2, [None, None, 0, 1]),
        (0, 0, []),
        (0, 5, list(range(5))),
        (3, 7, list(range(3, 7))),
        (9, 11, [9, None]),
        (10, 11, [None]),
        (11, 11, [])
    ]

    mylist = [i for i in range(23) if i % 2 == 0]

    for start, stop, _ in test_cases:
        x = list(none_slice_gabriel(mylist, start, stop))
        y = none_slice_elbiot(mylist, start, stop)

        assert x == y

if __name__ == '__main__':
    main()