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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_id_from_username(self, username):
 """Looks up a username's id :param string username: Username to lookup :returns: The id that matches username. """

        _mask = "mask[id, username]"
        _filter = {'users': {'username': utils.query_filter(username)}}
        user = self.list_users(_mask, _filter)
        if len(user) == 1:
            return [user[0]['id']]
        elif len(user) > 1:
            raise exceptions.SoftLayerError("Multiple users found with the name: %s" % username)
        else:
            raise exceptions.SoftLayerError("Unable to find user id for %s" % username)