quote accept two arguments: a string and safe characters. If you pass empty to quote as the second parameter, it means every characters except preserved characters will be replaced by a % leading characters, e.g. space will be replaced by %20, etc.

In my project, I invoke quote like quote(params, ''), and I have imported unicode_literals, so I passed a unicode parameter to quote method.

What will happen?

Next time you invoke quote with the same safe parameter you used before, you may get an error like UnicodeDecodeError: 'ascii' codec can't decode byte 0xe4 in position 0: ordinal not in range(128), urllib will cache the safe parameter(urllib.py 1277 line), it expects a byte type parameter but you pass an unicode one, also, that library didn’t check or convert it before it uses.

Best practice, pass a byte parameter like b'' to quote if you have same usage(unicode literals) like me.