security.py 文件源码

def safe_str_cmp(a, b):
    """This function compares strings in somewhat constant time.  This
    requires that the length of at least one string is known in advance.

    Returns `True` if the two strings are equal, or `False` if they are not.

    .. versionadded:: 0.7
    """
    if isinstance(a, text_type):
        a = a.encode('utf-8')
    if isinstance(b, text_type):
        b = b.encode('utf-8')

    if _builtin_safe_str_cmp is not None:
        return _builtin_safe_str_cmp(a, b)

    if len(a) != len(b):
        return False

    rv = 0
    if PY2:
        for x, y in izip(a, b):
            rv |= ord(x) ^ ord(y)
    else:
        for x, y in izip(a, b):
            rv |= x ^ y

    return rv == 0