matching unicode characters in python regular expressions

Question

I have read thru the other questions at Stackoverflow, but still no closer. Sorry, if this is allready answered, but I didn`t get anything proposed there to work.

>>> import re
>>> m = re.match(r'^/by_tag/(?P<tag>\w+)/(?P<filename>(\w|[.,!#%{}()@])+)$', '/by_tag/xmas/xmas1.jpg')
>>> print m.groupdict()
{'tag': 'xmas', 'filename': 'xmas1.jpg'}

All is well, then I try something with Norwegian characters in it ( or something more unicode-like ):

>>> m = re.match(r'^/by_tag/(?P<tag>\w+)/(?P<filename>(\w|[.,!#%{}()@])+)$', '/by_tag/påske/øyfjell.jpg')
>>> print m.groupdict()
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'groupdict'

How can I match typical unicode characters, like øæå? I`d like to be able to match those characters as well, in both the tag-group above and the one for filename.

• janbrohl: Make sure you normalize your strings because there are diffent codepoint-sequences generating the same visual apperance.

Answer 1

You need to specify the re.UNICODE flag, and input your string as a Unicode string by using the u prefix:

>>> re.match(r'^/by_tag/(?P<tag>\w+)/(?P<filename>(\w|[.,!#%{}()@])+)$', u'/by_tag/påske/øyfjell.jpg', re.UNICODE).groupdict()
{'tag': u'p\xe5ske', 'filename': u'\xf8yfjell.jpg'}

This is in Python 2; in Python 3 you must leave out the u because all strings are Unicode, and you can leave off the re.UNICODE flag.

• Tamm: +1 for: and input your string as a Unicode string by using the u prefix
• Charlie Parker: I don't understand, why do we need to pass in re.UNICODE? (I'm using python 3)
• Thomas: @CharlieParker Notice the date of this answer :) In Python 3, re.UNICODE does nothing.

Answer 2

You need the UNICODE flag:

m = re.match(r'^/by_tag/(?P<tag>\w+)/(?P<filename>(\w|[.,!#%{}()@])+)$', '/by_tag/påske/øyfjell.jpg', re.UNICODE)

• Kevin: Is it required for Python3 too?
• jeffhale: @Kevin - you don't need the unicode flag with Python 3. "Unicode matching is already enabled by default in Python 3 for Unicode (str) patterns..." - docs.python.org/3/howto/regex.html
• Charlie Parker: I don't understand, why do we need to pass in re.UNICODE? (I'm using python 3)

Answer 3

In Python 2, you need the re.UNICODE flag and the unicode string constructor

>>> re.sub(r"[\w]+","___",unicode(",./hello-=+","utf-8"),flags=re.UNICODE)
u',./___-=+'
>>> re.sub(r"[\w]+","___",unicode(",./cześć-=+","utf-8"),flags=re.UNICODE)
u',./___-=+'
>>> re.sub(r"[\w]+","___",unicode(",./привет-=+","utf-8"),flags=re.UNICODE)
u',./___-=+'
>>> re.sub(r"[\w]+","___",unicode(",./你好-=+","utf-8"),flags=re.UNICODE)
u',./___-=+'
>>> re.sub(r"[\w]+","___",unicode(",./你好,世界-=+","utf-8"),flags=re.UNICODE)
u',./___\uff0c___-=+'
>>> print re.sub(r"[\w]+","___",unicode(",./你好,世界-=+","utf-8"),flags=re.UNICODE)
,./___,___-=+

(In the latter case, the comma is Chinese comma.)

• Charlie Parker: I don't understand, why do we need to pass in re.UNICODE? (I'm using python 3)