I now realized LWPCookieJar is a subclass of CookieJar but it behaves differently. I believe there are other quirks I haven't discovered, like expire=None which cause exception in LWPCookieJar, but works fine for CookieJar. Sadly the doc didn't mention them.

The official python document introduced 2 file cookiejar, one is Mozilla's FileCookieJar, which is explicitly advised as depricated.
LWPCookieJar which is human-readable seems the only advisable chooice to me. But it turns out not that simple.
My guess is that not many people use this module, or the expire=None problem and this dot question should be quite easy to spot on google. 

So forks, could your suggest how does other python user deal with cookie storage. Do they just pickle the cookie objects and save to file?
Or any via 3rd party cookie batteries? What's their pro/cons ? 

LWPCookie's usage is strage to me and ,I believe, many average users, I guess many people like me will be willing to know alternatives.