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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 sys_hist(self, name=None, where=None):
 """ Return the effective total low and high histogram for a given systematic over samples in this channel. If a sample does not contain the named systematic then its nominal histogram is used for both low and high variations. Parameters name : string, optional (default=None) The systematic name otherwise nominal if None where : callable, optional (default=None) A callable taking one argument: the sample, and returns True if this sample should be included in the total. Returns ------- total_low, total_high : histograms The total low and high histograms for this systematic """

        total_low, total_high = None, None
        for sample in self.samples:
            if where is not None and not where(sample):
                continue
            low, high = sample.sys_hist(name)
            if total_low is None:
                total_low = low.Clone(shallow=True)
            else:
                total_low += low
            if total_high is None:
                total_high = high.Clone(shallow=True)
            else:
                total_high += high
        return total_low, total_high