I tested utf_16_32_surrogates_4.patch: surrogateescape with as encoder does not work as expected.

>>> b'[\x00\x80\xdc]\x00'.decode('utf-16-le', 'ignore')
'[]'
>>> b'[\x00\x80\xdc]\x00'.decode('utf-16-le', 'replace')
'[�]'
>>> b'[\x00\x80\xdc]\x00'.decode('utf-16-le', 'surrogateescape')
'[\udc80\udcdc\uffff'

=> I expected '[\udc80\udcdc]'.

With a decoder, surrogateescape does not work neither:

>>> '[\uDC80]'.encode('utf-16-le', 'surrogateescape')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'utf-16-le' codec can't encode character '\udc80' in position 1: surrogates not allowed

Using the PEP 383, I expect that data.decode(encoding, 'surrogateescape') does never fail, data.decode(encoding, 'surrogateescape').encode(encoding, 'surrogateescape') should give data.

--

With UTF-16, there is a corner case:

>>> b'[\x00\x00'.decode('utf-16-le', 'surrogateescape')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/haypo/prog/python/default/Lib/encodings/utf_16_le.py", line 16, in decode
    return codecs.utf_16_le_decode(input, errors, True)
UnicodeDecodeError: 'utf-16-le' codec can't decode byte 0x00 in position 2: truncated data
>>> b'[\x00\x80'.decode('utf-16-le', 'surrogateescape')
'[\udc80'

The incomplete sequence b'\x00' raises a decoder error, wheras b'\x80' does not. Should we extend the PEP 383 to bytes in range [0; 127]? Or should we keep this behaviour?

Sorry, this question is unrelated to this issue.