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Sorry, I reopened this issue because I found problem.

With attached "mbcs.py" and "mbcs.txt", result file
"hoge.txt" gets corrupted. This happens because Codec.decode
is called incrementally, while default value for final in
mbcs_decode() is True.

>I think the default value for final in mbcs_decode() should
>be true, so that the stateless decoder detects incomplete
>byte sequences too.

Probably this is not true. I think "stateless" means codec
doesn't have internal state for incremental usage, doesn't
mean it is not called incrementally.

# I hope attached "fix.patch" fixes the problem.