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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_access_token(self):
 """ Obtain the access token to access private resources at the API endpoint. """

        if self.access_token is None:
            request_token = self._get_rt_from_session()
            oauth = OAuth1(
                self.consumer_key,
                client_secret=self.consumer_secret,
                resource_owner_key=request_token['oauth_token'],
                resource_owner_secret=request_token['oauth_token_secret'])
            at_url = self.access_token_url
            # Passing along oauth_verifier is required according to:
            # http://groups.google.com/group/twitter-development-talk/browse_frm/thread/472500cfe9e7cdb9#
            # Though, the custom oauth_callback seems to work without it?
            oauth_verifier = get_request_param(self.request, 'oauth_verifier')
            if oauth_verifier:
                at_url = at_url + '?' + urlencode(
                    {'oauth_verifier': oauth_verifier})
            response = requests.post(url=at_url, auth=oauth)
            if response.status_code not in [200, 201]:
                raise OAuthError(
                    _('Invalid response while obtaining access token'
                      ' from "%s".') % get_token_prefix(
                          self.request_token_url))
            self.access_token = dict(parse_qsl(response.text))

            self.request.session['oauth_%s_access_token' % get_token_prefix(
                self.request_token_url)] = self.access_token
        return self.access_token