code: def get_access_token(self, code=None, **params):
          
          if self._access_token is None:
              if code is None:
                  raise ValueError(_('Invalid code.'))
              
              self.access_token_dict = self._get_access_token(code, **params)
              try:
                  self._access_token = self.access_token_dict['access_token']
              except KeyError, e:
                  raise OAuthError("Credentials could not be validated, the provider returned no access token.")
                  
          return self._access_token
docs: Return the memoized access token or go out and fetch one.