werkzeug里的safe_str_cmp函数意义是什么？
代码如下：def safe_str_cmp(a, b):
if isinstance(a, str):
a = a.encode("utf-8")
if isinstance(b, str):
b = b.encode("utf-8")
if len(a) != len(b):
return False
rv = 0
for x, y in zip(a, b):
rv |= x ^ y
return rv == 0
和 is 或 == 有什么不同？
注释为：
"""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
"""
在注释里没有看出来有对字符串进行什么特别的比较，请问大佬们，这个函数的意义何在呢？
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