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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 before(self, callback: Union[Callable, str]) -> "Control": """Register a control method that reacts before the trigger method is called. Parameters: callback: The control method. If given as a callable, then that function will be used as the callback. If given as a string, then the control will look up a method with that name when reacting (useful when subclassing). """

        if isinstance(callback, Control):
            callback = callback._before
        self._before = callback
        return self