When I do codecs.encode(codecs.decode('\xed\xbc\xad', 'utf8'), 'utf8') its not throwing an exception. '\xed\xbc\xad' is an invalid UTF8 byte sequence. It maps to the value U+DF2D which is a "surrogate pair" it seems. http://tools.ietf.org/html/rfc3629#section-4 explains: However, pairs of UCS-2 values between D800 and DFFF (surrogate pairs in Unicode parlance), being actually UCS-4 characters transformed through UTF-16, need special treatment: the UTF-16 transformation must be undone, yielding a UCS-4 character that is then transformed as above. which would suggest that it is invalid. However, I think wikipedia's explanation is a bit clearer: UTF-8 may only legally be used to encode valid Unicode scalar values. According to the Unicode standard the high and low surrogate halves used by UTF-16 (U+D800 through U+DFFF) and values above U+10FFFF are not legal Unicode values, and the UTF-8 encoding of them is an invalid byte sequence and should be treated as described above. Thanks, Mike

Sorry, meant to add this part to the quote from the rfc: This leads to different results for character numbers above 0xFFFF; the CESU-8 encoding of those characters is NOT valid UTF-8

This is already fixed in Python 3. However I think that for backward compatibility reasons it can't be fixed in Python 2, where it is possible to encode and decode every codepoint to/from UTF-8. See also http://bugs.python.org/issue8271#msg102209 I think this can be closed as wontfix.

Ezio Melotti wrote: > > I think this can be closed as wontfix. Agreed. I've already closed the ticket.