itsdangerous.py 文件源码

def constant_time_compare(val1, val2):
    """Returns True if the two strings are equal, False otherwise.

    The time taken is independent of the number of characters that match.  Do
    not use this function for anything else than comparision with known
    length targets.

    This is should be implemented in C in order to get it completely right.
    """
    if _builtin_constant_time_compare is not None:
        return _builtin_constant_time_compare(val1, val2)
    len_eq = len(val1) == len(val2)
    if len_eq:
        result = 0
        left = val1
    else:
        result = 1
        left = val2
    for x, y in izip(bytearray(left), bytearray(val2)):
        result |= x ^ y
    return result == 0