'Fetch the sequnce of public twitter.Status message for all users.
Args:
since_id:
Returns only public statuses with an ID greater than (that is,
more recent than) the specified ID. [Optional]
Returns:
An sequence of twitter.Status instances, one for each message'

def GetPublicTimeline(self, since_id=None):

    parameters = {}
    if since_id:
        parameters['since_id'] = since_id
    url = (TWITTER_API_ROOT + 'statuses/public_timeline.json')
    json = self._FetchUrl(url, parameters=parameters)
    data = simplejson.loads(json)
    self._CheckForTwitterError(data)
    return [Status.NewFromJsonDict(x) for x in data]
