Return the Parser object used to parse a particular URI.

        Parser objects are required to have only 'parse' and 'unparse' methods.

def parser_for(self, uri):
        """Return the Parser object used to parse a particular URI.

        Parser objects are required to have only 'parse' and 'unparse' methods.

        """
        return self._parsers.get(self.scheme_of(uri), DefaultURIParser)