[Python-Dev] Improve open() to support reading file starting with an unicode BOM
victor.stinner at haypocalc.com
Fri Jan 8 01:10:35 CET 2010
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
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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