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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 _pre_run(self, pre_run=None):
        " Called during `run`. "
        if pre_run:
            pre_run()

        # Process registered "pre_run_callables" and clear list.
        for c in self.pre_run_callables:
            c()
        del self.pre_run_callables[:]