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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 restrict(self, addr):
 """ Drop an address from the set of addresses this proxy is permitted to introduce. :param addr: The address to remove. """


        # Remove the address from the set
        ip_addr = _parse_ip(addr)
        if ip_addr is None:
            LOG.warn("Cannot restrict address %r from proxy %s: "
                     "invalid address" % (addr, self.address))
        else:
            self.excluded.add(addr)