gistfile1.py

import os
import requests
from requests_oauthlib import OAuth1

auth = OAuth1('*APP_KEY*', '*APP_SECRET*',
              '*OAUTH_TOKEN*', '*OAUTH_TOKEN_SECRET*',
              signature_type='auth_header')

file_ = open('/path/to/file/image.jpg', 'rb')

requests.post('https://api.twitter.com/1.1/statuses/update_with_media.json',
              data={'status': 'Hey'},
              files={'media': (os.path.basename(file_.name), file_)},
              auth=auth)