[issue8271] str.decode('utf8', 'replace') -- conformance with Unicode 5.2.0

[STINNER Victor]

STINNER Victor <victor.stinner at haypocalc.com> added the comment:

> I also found out that, according to RFC 3629, surrogates 
> are considered invalid and they can't be encoded/decoded, 
> but the UTF-8 codec actually does it.

Python2 does, but Python3 raises an error.

Python 2.7a4+ (trunk:79675, Apr  3 2010, 16:11:36)
>>> u"\uDC80".encode("utf8")
'\xed\xb2\x80'

Python 3.2a0 (py3k:79441, Mar 26 2010, 13:04:55)
>>> "\uDC80".encode("utf8")
UnicodeEncodeError: 'utf-8' codec can't encode character '\udc80' in position 0: surrogates not allowed

Deny encoding surrogates (in utf8) causes a lot of crashs in Python3, because most functions calling suppose that _PyUnicode_AsString() does never fail: see #6687 (and #8195 and a lot of other crashs). It's not a good idea to change it in Python 2.7, because it would require a huge work and we are close to the first beta of 2.7.

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nosy: +haypo

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