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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 client(self):
 """XMLRPC client for PyPI. Always returns the same instance. If the package is provided as a path to compressed source file, PyPI will not be used and the client will not be instantiated. Returns: XMLRPC client for PyPI or None. """

        if self.proxy:
            proxyhandler = urllib.ProxyHandler({"http": self.proxy})
            opener = urllib.build_opener(proxyhandler)
            urllib.install_opener(opener)
            transport = ProxyTransport()
        if not hasattr(self, '_client'):
            transport = None
            if self.pypi:
                if self.proxy:
                    logger.info('Using provided proxy: {0}.'.format(
                        self.proxy))
                self._client = xmlrpclib.ServerProxy(settings.PYPI_URL,
                                                     transport=transport)
                self._client_set = True
            else:
                self._client = None

        return self._client