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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 user(self, username=None):
 """A user resource that represents a registered user in the portal."""

        if username is None:
            username = self.__getUsername()
        parsedUsername = urlparse.quote(username)
        url = self.root + "/%s" % parsedUsername
        return User(url=url,
                    securityHandler=self._securityHandler,
                    proxy_url=self._proxy_url,
                    proxy_port=self._proxy_port,
                    initialize=False)