Turn a string into a valid filename?

Question

I have a string that I want to use as a filename, so I want to remove all characters that wouldn't be allowed in filenames, using Python.

I'd rather be strict than otherwise, so let's say I want to retain only letters, digits, and a small set of other characters like "_-.() ". What's the most elegant solution?

The filename needs to be valid on multiple operating systems (Windows, Linux and Mac OS) - it's an MP3 file in my library with the song title as the filename, and is shared and backed up between 3 machines.

Answer 1

You can look at the Django framework for how they create a "slug" from arbitrary text. A slug is URL- and filename- friendly.

The Django text utils define a function, slugify(), that's probably the gold standard for this kind of thing. Essentially, their code is the following.

import unicodedata import re  def slugify(value, allow_unicode=False):     """     Taken from https://github.com/django/django/blob/master/django/utils/text.py     Convert to ASCII if 'allow_unicode' is False. Convert spaces or repeated     dashes to single dashes. Remove characters that aren't alphanumerics,     underscores, or hyphens. Convert to lowercase. Also strip leading and     trailing whitespace, dashes, and underscores.     """     value = str(value)     if allow_unicode:         value = unicodedata.normalize('NFKC', value)     else:         value = unicodedata.normalize('NFKD', value).encode('ascii', 'ignore').decode('ascii')     value = re.sub(r'[^\w\s-]', '', value.lower())     return re.sub(r'[-\s]+', '-', value).strip('-_') 

And the older version:

def slugify(value):     """     Normalizes string, converts to lowercase, removes non-alpha characters,     and converts spaces to hyphens.     """     import unicodedata     value = unicodedata.normalize('NFKD', value).encode('ascii', 'ignore')     value = unicode(re.sub('[^\w\s-]', '', value).strip().lower())     value = unicode(re.sub('[-\s]+', '-', value))     # ...     return value 

There's more, but I left it out, since it doesn't address slugification, but escaping.