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

There is a nice project on Github called python-slugify:

Install:

pip install python-slugify

Then use:

>>> from slugify import slugify
>>> txt = "This\ is/ a%#$ test ---"
>>> slugify(txt)
'this-is-a-test'

Answer 2

Just to further complicate things, you are not guaranteed to get a valid filename just by removing invalid characters. Since allowed characters differ on different filenames, a conservative approach could end up turning a valid name into an invalid one. You may want to add special handling for the cases where:

• The string is all invalid characters (leaving you with an empty string)

• You end up with a string with a special meaning, eg "." or ".."

• On windows, certain device names are reserved. For instance, you can't create a file named "nul", "nul.txt" (or nul.anything in fact) The reserved names are:

  CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9

You can probably work around these issues by prepending some string to the filenames that can never result in one of these cases, and stripping invalid characters.

Answer 3

You can use list comprehension together with the string methods.

>>> s
'foo-bar#baz?qux@127/\\9]'
>>> "".join(x for x in s if x.isalnum())
'foobarbazqux1279'

Answer 4

In one line:

valid_file_name = re.sub('[^\w_.)( -]', '', any_string)

you can also put '_' character to make it more readable (in case of replacing slashs, for example)

Answer 5

Keep in mind, there are actually no restrictions on filenames on Unix systems other than

• It may not contain \0
• It may not contain /

Everything else is fair game.

$ touch "
> even multiline
> haha
> ^[[31m red ^[[0m
> evil"
$ ls -la 
-rw-r--r--       0 Nov 17 23:39 ?even multiline?haha??[31m red ?[0m?evil
$ ls -lab
-rw-r--r--       0 Nov 17 23:39 \neven\ multiline\nhaha\n\033[31m\ red\ \033[0m\nevil
$ perl -e 'for my $i ( glob(q{./*even*}) ){ print $i; } '
./
even multiline
haha
 red 
evil

Yes, i just stored ANSI Colour Codes in a file name and had them take effect.

For entertainment, put a BEL character in a directory name and watch the fun that ensues when you CD into it ;)

Answer 6

I'm sure this isn't a great answer, since it modifies the string it's looping over, but it seems to work alright:

import string
for chr in your_string:
 if chr == ' ':
   your_string = your_string.replace(' ', '_')
 elif chr not in string.ascii_letters or chr not in string.digits:
    your_string = your_string.replace(chr, '')