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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 portal(self, portalID=None):
 """returns a specific reference to a portal"""

        if portalID is None:
            portalID = self.portalSelf.id
        url = "%s/%s" % (self.root, portalID)
        return Portal(url=url,
                  securityHandler=self._securityHandler,
                  proxy_url=self._proxy_url,
                  proxy_port=self._proxy_port,
                  initalize=True)