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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_vpnv4fs_table(self):
 """Returns global VPNv4 Flow Specification table. Creates the table if it does not exist. """

        vpnv4fs_table = self._global_tables.get(RF_VPNv4_FLOWSPEC)
        # Lazy initialization of the table.
        if not vpnv4fs_table:
            vpnv4fs_table = VPNv4FlowSpecTable(self._core_service,
                                               self._signal_bus)
            self._global_tables[RF_VPNv4_FLOWSPEC] = vpnv4fs_table
            self._tables[(None, RF_VPNv4_FLOWSPEC)] = vpnv4fs_table

        return vpnv4fs_table