[Answer]-Python Oauth Request to Twitter Yields Response 403 – SSL is Required

Here:

request_token_url = 'http://api.twitter.com/oauth/request_token'
access_token_url = 'http://api.twitter.com/oauth/access_token'

These requests need to be via https://

So

request_token_url = 'https://api.twitter.com/oauth/request_token'
access_token_url = 'https://api.twitter.com/oauth/access_token'

Should do the trick.