New submission from Wim:
Encoding a (well-formed) Unicode string containing a non-BMP character, using
the xmlcharrefreplace error handler, will produce two XML entities for
surrogate codepoints instead of one entity for the actual character.
Here's a transcript (Python 2.7.3, x86_64):
>>> b = '\xf0\x9f\x92\x9d'
>>> u = b.decode('utf8')
>>> u
u'\U0001f49d'
>>> u.encode('ascii', errors='xmlcharrefreplace')
'��'
>>> ( u'\U0001f49d' ).encode('ascii', errors='xmlcharrefreplace')
'��'
>>> list(u)
[u'\ud83d', u'\udc9d']
>>> u.encode('utf8', errors='xmlcharrefreplace')
'\xf0\x9f\x92\x9d'
The utf8 bytestring is correctly decoded, and the print representation shows
one single Unicode character. Encoding using xmlcharrefreplace produces two XML
entities, which is wrong[1]: a single non-BMP character should be represented
in XML as a single entity reference, in this case presumably '💝'.
As the last two lines show, I'm using a narrow build (so the unicode strings
are represented internally in UTF-16, I guess). Converting the string back to
utf8 does the right thing, and emits a single UTF8 sequence representing the
supplementary-plane codepoint.
(FWIW, the backslashreplace error handler also emits a surrogate pair, but I
don't know if there is a complete specification for what that handler does, so
it's possible that it's not wrong.)
[1] http://www.w3.org/International/questions/qa-escapes#bytheway
----------
components: Library (Lib), Unicode
messages: 169886
nosy: ezio.melotti, wiml
priority: normal
severity: normal
status: open
title: encode(..., 'xmlcharrefreplace') produces entities for surrogate pairs
type: behavior
versions: Python 2.7
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue15866>
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