Adds a suitable extension to every file in the current folder

automime.py

import mimetypes
import os
import sys

import magic


try:
    dir = sys.argv[1]
except IndexError:
    dir = os.getcwd()

files = [f for f in os.listdir(dir)
         if os.path.isfile(os.path.join(dir, f))]

for file in files:
    if file == sys.argv[0]:
        continue
    mimetype = magic.from_file(file, mime=True)
    extension = mimetypes.guess_extension(mimetype)
    if extension and not file.endswith(extension):
        os.rename(file, file + extension)