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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 get_url(self, url):
 """ Internally used to retrieve the contents of a URL """

        _r = self.br.open(url)

        # check that we've not been redirected to the login page
        if self.br.geturl().startswith(self.AUTH_URL):
            raise AuthRequiredException
        elif self.br.geturl().startswith(self.ERROR_URL):
            raise RequestErrorException
        else:
            return _r.read()