'Befriends the user specified by the user_id or screen_name.
The twitter.Api instance must be authenticated.
Args:
user_id:
A user_id to follow [Optional]
screen_name:
A screen_name to follow [Optional]
follow:
Set to False to disable notifications for the target user
Returns:
A twitter.User instance representing the befriended user.'

def CreateFriendship(self, user_id=None, screen_name=None, follow=True):

    url = ('%s/friendships/create.json' % self.base_url)
    data = {}
    if user_id:
        data['user_id'] = user_id
    elif screen_name:
        data['screen_name'] = screen_name
    else:
        raise TwitterError('Specify    at    least    one    of    user_id    or    screen_name.')
    if follow:
        data['follow'] = 'true'
    else:
        data['follow'] = 'false'
    json = self._FetchUrl(url, post_data=data)
    data = self._ParseAndCheckTwitter(json)
    return User.NewFromJsonDict(data)
