Semver 2.0.0 compatible version comparison w/o regexes

semver.py

def compare(a, b):
    """
    Compare two version strings. 
    :return -1, 0, 1
    :rtype: int
    """
    a = map(_cast_int, a.split('+', 2)[0].split('.'))
    b = map(_cast_int, b.split('+', 2)[0].split('.'))
    c = _cmp_range(a[:3], b[:3])
    if c != 0:
        return c
    c = _cmp_range(a[3:], b[3:], flip=True)
    if c != 0:
        return c
    if not a[3:]:
        return 1
    if not b[3:]:
        return -1
    return c


def _cmp_range(a, b, flip=False):
    for i in range(min(len(a), len(b))):
        aa = a[i]
        bb = b[i]
        c = _compare_item(aa, bb, flip)
        if c == 0:
            continue
        return c
    return cmp(len(a), len(b))


def _cast_int(a):
    try:
        return int(a)
    except:
        return a


def _compare_item(a, b, flip=False):
    if isinstance(a, int) and isinstance(b, int):
        return cmp(a, b)
    elif isinstance(a, int):
        return -1 if flip else 1
    elif isinstance(b, int):
        return 1 if flip else -1
    else:
        return cmp(a, b)