I'm really confused with the
codecs.open function. When I do:
file = codecs.open("temp", "w", "utf-8") file.write(codecs.BOM_UTF8) file.close()
It gives me the error
UnicodeDecodeError: 'ascii' codec can't decode byte 0xef in position 0: ordinal not in range(128)
If I do:
file = open("temp", "w") file.write(codecs.BOM_UTF8) file.close()
It works fine.
Question is why does the first method fail? And how do I insert the bom?
If the second method is the correct way of doing it, what the point of using
codecs.open(filename, "w", "utf-8")?
I believe the problem is that
codecs.BOM_UTF8 is a byte string, not a Unicode string. I suspect the file handler is trying to guess what you really mean based on "I'm meant to be writing Unicode as UTF-8-encoded text, but you've given me a byte string!"
Try writing the Unicode string for the byte order mark (i.e. Unicode U+FEFF) directly, so that the file just encodes that as UTF-8:
import codecs file = codecs.open("lol", "w", "utf-8") file.write(u'\ufeff') file.close()
(That seems to give the right answer - a file with bytes EF BB BF.)
EDIT: S. Lott's suggestion of using "utf-8-sig" as the encoding is a better one than explicitly writing the BOM yourself, but I'll leave this answer here as it explains what was going wrong before.
Read the following: http://docs.python.org/library/codecs.html#module-encodings.utf_8_sig
with codecs.open("test_output", "w", "utf-8-sig") as temp: temp.write("hi mom\n") temp.write(u"This has ♭")
The resulting file is UTF-8 with the expected BOM.