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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def Draw(self, *args, **kwargs):
 """ Loop over subfiles, draw each, and sum the output into a single histogram. """

        self.reset()
        output = None
        while self._rollover():
            if output is None:
                # Make our own copy of the drawn histogram
                output = self._tree.Draw(*args, **kwargs)
                if output is not None:
                    output = output.Clone()
                    # Make it memory resident (histograms)
                    if hasattr(output, 'SetDirectory'):
                        output.SetDirectory(0)
            else:
                newoutput = self._tree.Draw(*args, **kwargs)
                if newoutput is not None:
                    if isinstance(output, _GraphBase):
                        output.Append(newoutput)
                    else:  # histogram
                        output += newoutput
        return output