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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 vrfs_get(self, subcommand='routes', route_dist=None, route_family='all', format='json'):
 """ This method returns the existing vrfs. ``subcommand`` specifies one of the following. - 'routes': shows routes present for vrf - 'summary': shows configuration and summary of vrf ``route_dist`` specifies a route distinguisher value. If route_family is not 'all', this value must be specified. ``route_family`` specifies route family of the VRF. This parameter must be one of the following. - RF_VPN_V4 = 'ipv4' - RF_VPN_V6 = 'ipv6' - RF_L2_EVPN = 'evpn' - 'all' (default) ``format`` specifies the format of the response. This parameter must be one of the following. - 'json' (default) - 'cli' """

        show = {
            'format': format,
        }
        if route_family in SUPPORTED_VRF_RF:
            assert route_dist is not None
            show['params'] = ['vrf', subcommand, route_dist, route_family]
        else:
            show['params'] = ['vrf', subcommand, 'all']

        return call('operator.show', **show)