def outputAlphabet(self):
        """
        The full set of symbols which can be produced by this automaton.
        """
        return set(
            chain.from_iterable(
                outputSymbols for
                (inState, inputSymbol, outState, outputSymbols)
                in self._transitions
            )
        )

        The full set of symbols which can be produced by this automaton.
        
stackoverflow/venv/lib/python3.6/site-packages/automat/_core.py