def trace(self, trace=2):
        self._trace = trace

    # TODO: change this to conform more with the standard ChartParser
L{app.AppLogger.stop} removes the observer created in C{start}, and
dataset/ETHPy150Open nltk/nltk/nltk/parse/pchart.py/BottomUpProbabilisticChartParser.trace--crossover with--dataset/ETHPy150Open twisted/twisted/twisted/test/test_twistd.py/AppLoggerTests.test_stop