'Creates a subscription to a list by the authenticated user.
Args:
owner_screen_name (str, optional):
The screen_name of the user who owns the list being requested
by a slug.
owner_id (int, optional):
The user ID of the user who owns the list being requested
by a slug.
list_id (int, optional):
The numerical id of the list.
slug (str, optional):
You can identify a list by its slug instead of its numerical id.
If you decide to do so, note that you\'ll also have to specify
the list owner using the owner_id or owner_screen_name parameters.
Returns:
twitter.user.User: A twitter.User instance representing the user subscribed'

def CreateSubscription(self, owner_screen_name=False, owner_id=False, list_id=None, slug=None):

    url = ('%s/lists/subscribers/create.json' % self.base_url)
    parameters = {}
    parameters.update(self._IDList(list_id=list_id, slug=slug, owner_id=owner_id, owner_screen_name=owner_screen_name))
    resp = self._RequestUrl(url, 'POST', data=parameters)
    data = self._ParseAndCheckTwitter(resp.content.decode('utf-8'))
    return User.NewFromJsonDict(data)
