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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 _redistribute_builder(self, afi='ipv4', source=None):
 """Build BGP redistribute method. Do not use this method directly. You probably want ``redistribute``. Args: source (str):
 Source for redistributing. (connected) afi (str):
 Address family to configure. (ipv4, ipv6) Returns: Method to redistribute desired source. Raises: KeyError: if `source` is not specified. Examples: Traceback (most recent call last):
 AttributeError """

        if source == 'connected':
            return getattr(self._rbridge,
                           'rbridge_id_router_router_bgp_address_family_{0}_'
                           '{0}_unicast_default_vrf_af_{0}_uc_and_vrf_cmds_'
                           'call_point_holder_redistribute_connected_'
                           'redistribute_connected'.format(afi))
        # TODO: Add support for 'static' and 'ospf'
        else:
            raise AttributeError('Invalid source.')