pgsql: Perform conversion from Python unicode to string/bytes object vi

Perform conversion from Python unicode to string/bytes object via UTF-8.

We used to convert the unicode object directly to a string in the server
encoding by calling Python's PyUnicode_AsEncodedString function. In other
words, we used Python's routines to do the encoding. However, that has a
few problems. First of all, it required keeping a mapping table of Python
encoding names and PostgreSQL encodings. But the real killer was that Python
doesn't support EUC_TW and MULE_INTERNAL encodings at all.

Instead, convert the Python unicode object to UTF-8, and use PostgreSQL's
encoding conversion functions to convert from UTF-8 to server encoding. We
were already doing the same in the other direction in PLyUnicode_FromString,
so this is more consistent, too.

Note: This makes SQL_ASCII to behave more leniently. We used to map
SQL_ASCII to Python's 'ascii', which on Python means strict 7-bit ASCII
only, so you got an error if the python string contained anything but pure
ASCII. You no longer get an error; you get the UTF-8 representation of the
string instead.

Backpatch to 9.0, where these conversions were introduced.

Jan Urbański

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/31595993901484d24c9ba62428c7abec207dd55e

Modified Files
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src/pl/plpython/expected/plpython_unicode_3.out | 54 -------------
src/pl/plpython/plpython.c | 98 ++++++++++-------------
2 files changed, 44 insertions(+), 108 deletions(-)