def start(self):
        """Start collecting trace information."""
        if self._collectors:
            self._collectors[-1].pause()
        self._collectors.append(self)
        #print("Started: %r" % self._collectors, file=sys.stderr)

        # Check to see whether we had a fullcoverage tracer installed.
        traces0 = []
        if hasattr(sys, "gettrace"):
            fn0 = sys.gettrace()
            if fn0:
                tracer0 = getattr(fn0, '__self__', None)
                if tracer0:
                    traces0 = getattr(tracer0, 'traces', [])

        # Install the tracer on this thread.
        fn = self._start_tracer()

        for args in traces0:
            (frame, event, arg), lineno = args
            try:
                fn(frame, event, arg, lineno=lineno)
            except __HOLE__:
                raise Exception(
                    "fullcoverage must be run with the C trace function."
                )

        # Install our installation tracer in threading, to jump start other
        # threads.
        threading.settrace(self._installation_trace)
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/coverage/collector.py/Collector.start