def step(self):
        if self._chart is None:
            raise ValueError('Parser must be initialized first')
        while True:
            self._restart = False
            w = 50 // (self._chart.num_leaves()+1)

            for e in self._parse():
                if self._trace > 1: print(self._current_chartrule)
                if self._trace > 0: print(self._chart.pretty_format_edge(e,w))
                yield e
                if self._restart: break
            else:
                yield None # No more edges.
Return a generator that adds edges to the chart, one at a
dataset/ETHPy150Open nltk/nltk/nltk/parse/chart.py/SteppingChartParser.step