Write to UTF-8 file in Python

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 codecsfile = 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

Do this

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.

@S-Lott gives the right procedure, but expanding on the Unicode issues, the Python interpreter can provide more insights.

Jon Skeet is right (unusual) about the codecs module - it contains byte strings:

>>> import codecs>>> codecs.BOM'\xff\xfe'>>> codecs.BOM_UTF8'\xef\xbb\xbf'>>> 

Picking another nit, the BOM has a standard Unicode name, and it can be entered as:

>>> bom= u"\N{ZERO WIDTH NO-BREAK SPACE}">>> bomu'\ufeff'

It is also accessible via unicodedata:

>>> import unicodedata>>> unicodedata.lookup('ZERO WIDTH NO-BREAK SPACE')u'\ufeff'>>>