<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_user_data(self):
 """ Base method for retrieving user data from a viz. """


        url = self.session.host + '/sessions/' + str(self.session.id) + '/visualizations/' + str(self.id) + '/settings/'
        r = requests.get(url)
        if r.status_code == 200:
            content = r.json()
        else:
            raise Exception('Error retrieving user data from server')

        return content