[Python-Dev] Improve open() to support reading file starting with an unicode BOM
Henning von Bargen
henning.vonbargen at arcor.de
Sun Jan 10 12:10:02 CET 2010
If Python should support BOM when reading text files,
it should also be able to *write* such files.
An encoding="BOM" argument wouldn't help here, because
it does not specify which encoding to use actually:
UFT-8, UTF-16-LE or what?
That would be a point against encoding="BOM" and
pro an additional keyword argument "use_bom" or whatever
with the following values:
None: default (old) behaviour: don't handle BOM at all
True: reading: expect BOM (raising an exception if it's
missing). The encoding argument must be None
or it must match the encoding implied by the
writing: write a BOM. The encoding argument must be
one of the UTF encodings.
False: reading: If a BOM is present, use it to determine the
file encoding. The encoding argument must
be None or it must match the encoding implied by
the BOM. (*)
Otherwise, use the encoding argument to determine
writing: do not write a BOM. Use the encoding argument.
(*) This is a question of taste. I think some people would prefer
a fourth value "AUTO" instead, or to swap the behaviour of
None and False.
P.S. To make things worse, I have sometimes seen XML files with a
UTF-8 BOM, but an XML encoding declaration of "iso-8859-1".
For such files, whatever you guess will be wrong anyway...
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