get_random_file.py

import os
from fnmatch import fnmatch
import random

def get_random_file(folder, *extensions):
    """
    get_random_file('/foo/bar', '*.jpg')
    """
    files = [os.path.join(folder, fname) for fname in os.listdir(folder)]
    pictures  = [fpath for fpath in files if any([fnmatch(fpath, ext) for ext in extensions])]
    return random.choice(pictures)