Normalizing unicode text to filenames, etc. in Python

Question

Are there any standalonenish solutions for normalizing international unicode text to safe ids and filenames in Python?

E.g. turn My International Text: åäö

Answer 1

The way to solve this problem is to make a decision on which characters are allowed (different systems have different rules for valid identifiers.

Once you decide on which characters are allowed, write an allowed() predicate and a dict subclass for use with str.translate:

def makesafe(text, allowed, substitute=None):
    ''' Remove unallowed characters from text.
        If *substitute* is defined, then replace
        the character with the given substitute.
    '''
    class D(dict):
        def __getitem__(self, key):
            return key if allowed(chr(key)) else substitute
    return text.translate(D())

This function is very flexible. It let's you easily specify rules for deciding which text is kept and which text is either replaced or removed.

Here's a simple example using the rule, "only allow characters that are in the unicode category L":

import unicodedata

def allowed(character):
    return unicodedata.category(character).startswith('L')

print(makesafe('the*ides&of*march', allowed, '_'))
print(makesafe('the*ides&of*march', allowed))

That code produces safe output as follows:

the_ides_of_march
theidesofmarch