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The various attempts by RFCs to codify HTTP cookies are useless and bear no resemblance to what browsers actually do.
In the real world, every byte in the range 0x20-0x7E is allowed, except for the semicolon, the equals (in names), and in Opera, in some places, the double-quote. Many browsers even allow most of the control codes! The question of non-ASCII Unicode characters is tricky, but none of them cause a token break.
Contrary to RFC2109 and its successors, no browser takes any notice of quoted-string cookies or backslash-escaping, so the effort Cookie.py puts into producing an encoded string and 'parsing' input cookies is completely wasted. It should do what everyone else does: split on semicolon, left-strip the whitespace, split each cookie on first equals.
(In reality cookie names and values have no inherent encoding scheme, so if you want to include out-of-band characters like semicolon, control characters or non-ASCII characters you have to use an ad-hoc encoding scheme, often URL-encoding.)