Guido van Rossum wrote:
I'm a little hesitant about this. First of all, UTF-8 + BOM is crazy
talk. And for the other two, perhaps it would make more sense to have
a separate encoding-guessing function that takes a binary stream and
returns a text stream wrapping it with the proper encoding?

Alternatively, have a universal UTF-8/16/32 encoding, ie one that expects UTF-8,
with or without BOM, or UTF-16/32 with BOM.

On Thu, Jan 7, 2010 at 4:10 PM, Victor Stinner
<victor.stin...@haypocalc.com> wrote:
Hi,

Builtin open() function is unable to open an UTF-16/32 file starting with a
BOM if the encoding is not specified (raise an unicode error). For an UTF-8
file starting with a BOM, read()/readline() returns also the BOM whereas the
BOM should be "ignored".

See recent issues related to reading an UTF-8 text file including a BOM: #7185
(csv) and #7519 (ConfigParser). Such file can be opened in unicode mode with
the UTF-8-SIG encoding, but it's possible to do better.

I propose to improve open() (TextIOWrapper) by using the BOM to choose the
right encoding. I think that only files opened in read only mode should
support this new feature. *Read* the BOM in a *write* only file would cause
unexpected behaviours.

Since my proposition changes the result TextIOWrapper.read()/readline() for
files starting with a BOM, we might introduce an option to open() to enable
the new behaviour. But is it really needed to keep the backward compatibility?

I wrote a proof of concept attached to the issue #7651. My patch only changes
the behaviour of TextIOWrapper for reading files starting with a BOM. It
doesn't work yet if a seek() is used before the first read.

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