What is the best way to remove accents (normalize) in a Python unicode string?

How about this:

import unicodedata
def strip_accents(s):
   return ''.join(c for c in unicodedata.normalize('NFD', s)
                  if unicodedata.category(c) != 'Mn')

This works on greek letters, too:

>>> strip_accents(u"A \u00c0 \u0394 \u038E")
u'A A \u0394 \u03a5'
>>> 

The character category "Mn" stands for Nonspacing_Mark, which is similar to unicodedata.combining in MiniQuark's answer (I didn't think of unicodedata.combining, but it is probably the better solution, because it's more explicit).

And keep in mind, these manipulations may significantly alter the meaning of the text. Accents, Umlauts etc. are not "decoration".

I just found this answer on the Web:

import unicodedata

def remove_accents(input_str):
    nfkd_form = unicodedata.normalize('NFKD', input_str)
    only_ascii = nfkd_form.encode('ASCII', 'ignore')
    return only_ascii

It works fine (for French, for example), but I think the second step (removing the accents) could be handled better than dropping the non-ASCII characters, because this will fail for some languages (Greek, for example). The best solution would probably be to explicitly remove the unicode characters that are tagged as being diacritics.

Edit: this does the trick:

import unicodedata

def remove_accents(input_str):
    nfkd_form = unicodedata.normalize('NFKD', input_str)
    return u"".join([c for c in nfkd_form if not unicodedata.combining(c)])

unicodedata.combining(c) will return true if the character c can be combined with the preceding character, that is mainly if it's a diacritic.

Edit 2: remove_accents expects a unicode string, not a byte string. If you have a byte string, then you must decode it into a unicode string like this:

encoding = "utf-8" # or iso-8859-15, or cp1252, or whatever encoding you use
byte_string = b"café"  # or simply "café" before python 3.
unicode_string = byte_string.decode(encoding)

Actually I work on project compatible python 2.6, 2.7 and 3.4 and I have to create IDs from free user entries.

Thanks to you, I have created this function that works wonders.

import re
import unicodedata

def strip_accents(text):
    """
    Strip accents from input String.

    :param text: The input string.
    :type text: String.

    :returns: The processed String.
    :rtype: String.
    """
    try:
        text = unicode(text, 'utf-8')
    except (TypeError, NameError): # unicode is a default on python 3 
        pass
    text = unicodedata.normalize('NFD', text)
    text = text.encode('ascii', 'ignore')
    text = text.decode("utf-8")
    return str(text)

def text_to_id(text):
    """
    Convert input text to id.

    :param text: The input string.
    :type text: String.

    :returns: The processed String.
    :rtype: String.
    """
    text = strip_accents(text.lower())
    text = re.sub('[ ]+', '_', text)
    text = re.sub('[^0-9a-zA-Z_-]', '', text)
    return text

result:

text_to_id("Montréal, über, 12.89, Mère, Françoise, noël, 889")
>>> 'montreal_uber_1289_mere_francoise_noel_889'

Unidecode is the correct answer for this. It transliterates any unicode string into the closest possible representation in ascii text.

Example:

accented_string = u'Málaga'
# accented_string is of type 'unicode'
import unidecode
unaccented_string = unidecode.unidecode(accented_string)
# unaccented_string contains 'Malaga'and is of type 'str'