New listdirs

listdirs_new.py

import os
from typing import List, Union


def listdirs(path, extensions: Union[List[str], str] = None):
    """ List all files in directory (including walking all subdirectories).

    Can filter by file extension by providing either, for example:
        extensions='png'
        extensions=['png', 'jpeg']

    """
    output = []
    for root, dirs, files in os.walk(path):
        for file in files:
            output.append(os.path.join(root, file))

    if extensions:
        if isinstance(extensions, str):
            extensions = [extensions]

        def filter_ext(f):
            return True if os.path.splitext(f)[-1].strip('.') in extensions else False

        output = list(filter(filter_ext, output))

    return output