On 8/28/2014 12:30 AM, MRAB wrote:
On 2014-08-28 05:56, Glenn Linderman wrote:
On 8/27/2014 6:08 PM, Stephen J. Turnbull wrote:
Glenn Linderman writes:
  > On 8/26/2014 4:31 AM, MRAB wrote:
  > > On 2014-08-26 03:11, Stephen J. Turnbull wrote:
  > >> Nick Coghlan writes:

  > > How about:
  > >
  > >     replace_surrogate_escapes(s, replacement='\uFFFD')
  > >
  > > If you want them removed, just pass an empty string as the
  > > replacement.

That seems better to me (I had too much C for breakfast, I think).

  > And further, replacement could be a vector of 128 characters, to do
  > immediate transcoding,

Using what encoding?

The vector would contain the transcoding. Each lone surrogate would map
to a character in the vector.

If you knew that much, why didn't you use
(write, if necessary) an appropriate codec?  I can't envision this
being useful.

If the data format describes its encoding, possibly containing data from
several encodings in various spots, then perhaps it is best read as
binary, and processed as binary until those definitions are found.

But an alternative would be to read with surrogate escapes, and then
when the encoding is determined, to transcode the data. Previously, a
proposal was made to reverse the surrogate escapes to the original
bytes, and then apply the (now known) appropriate codec. There are not
appropriate codecs that can convert directly from surrogate escapes to
the desired end result. This technique could be used instead, for
single-byte, non-escaped encodings. On the other hand, writing specialty
codecs for the purpose would be more general.

There'll be a surrogate escape if a byte couldn't be decoded, but just
because a byte could be decoded, it doesn't mean that it's correct.

If you picked the wrong encoding, the other codepoints could be wrong
too.

Aha! Thanks for pointing out the flaw in my reasoning. But that means it is also pretty useless to "replace_surrogate_escapes" at all, because it only cleans out the non-decodable characters, not the incorrectly decoded characters.