09.01.18 23:15, Rob Speer пише:

For the sake of discussion, let's call this encoding "web-1252". WHATWG calls it "windows-1252", 

notice that it's subtly different from Python's "windows-1252" encoding.. Python's windows-1252 has bytes that are undefined:

 >>> b'\x90'.decode('windows-1252')
UnicodeDecodeError: 'charmap' codec can't decode byte 0x90 in position 0: character maps to <undefined>

In web-1252, the bytes that are undefined according to windows-1252 map to the control characters in those positions in iso-8859-1 -- that is, the Unicode codepoints with the same number as the byte. In web-1252, b'\x90' would decode as '\u0090'.

This may seem like a silly encoding that encourages doing horrible things with text. That's pretty much the case. But there's a reason every Web browser implements it:

- It's compatible with windows-1252
- Any sequence of bytes can be round-tripped through it without losing information

It's not just this one encoding. WHATWG's encoding standard (https://encoding.spec.whatwg.org/ <https://encoding..spec.whatwg.org/>) contains modified versions of windows-1250 through windows-1258 and windows-874.

The way of solving this issue in Python is using an error handler. The "surrogateescape" error handler is specially designed for lossless reversible decoding. It maps every unassigned byte in the range 0x80-0xff to a single character in the range U+dc80-U+dcff. This allows you to distinguish correctly decoded characters from the escaped bytes, perform character by character processing of the decoded text, and encode the result back with the same encoding.

>>> b'\x90\x91\x92\x93'.decode('windows-1252', 'surrogateescape')
'\udc90‘’“'
>>> '\udc90‘’“'.encode('windows-1252', 'surrogateescape')
b'\x90\x91\x92\x93'

If you want to map unassigned bytes to other characters, you should just create a new error handler. There are caveats, since such characters are not distinguished from correctly decoded characters.

The same problem with the UTF-8 encoding. WHATWG allows encoding and decoding surrogate characters in the range U+d800-U+dcff. This is contrary to the Unicode Standard and raises an error by default in Python. But you can allow encoding and decoding of surrogate characters by explicitly specifying the "surrogatepass" error handler.

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