unique_filenames.py

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
"""Generate unique filenames for a file you're about to create.

The functions in this snippet are useful for ensuring you don't inadvertently
create a file that replaces an existing file.  Given a name, they try to
find a similar name that doesn't already exist on the disk.

This code isn't safe from race conditions -- if a file pops into existence
between the check and the write, you could still lose data -- but it's a
good start.  If you really want to be sure a file doesn't exist when you
write to it, use the 'x' mode for `open()` in Python 3:
https://alexwlchan.net/2016/03/exclusive-create-python/

"""

import os
import random
import string


def generate_variations(path):
    """Given a path, generate variations that add a few characters of random
    noise to the path.

    :param path: Starting path.

    """
    # Implementation note: the 'noise' is five characters of alphanumeric
    # text added before the file extension.  Including uppercase and lowercase,
    # this allows up to 62^5 = 9e9 possible variations.  That's plenty for
    # most use cases.  Add more characters if you're feeling picky.
    yield path
    base, ext = os.splitext(path)
    while True:
        noise = ''.join([
            random.choice(string.ascii_letters + string.digits)
            for _ in range(5)
        ])
        yield '%s_%s%s' % (base, noise, ext)


def choose_unique_filename(path):
    """Given a filename, return a variation on that filename that doesn't
    already exist on disk."""
    for new_path in generate_variations(path):
        if not os.path.exists(new_path):
            return new_path