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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 setup(self, proxystr='', prompting=True):
 """ Sets the proxy handler given the option passed on the command line. If an empty string is passed it looks at the HTTP_PROXY environment variable. """

        self.prompting = prompting
        proxy = self.get_proxy(proxystr)
        if proxy:
            proxy_support = urllib2.ProxyHandler({"http": proxy, "ftp": proxy})
            opener = urllib2.build_opener(proxy_support, urllib2.CacheFTPHandler)
            urllib2.install_opener(opener)