<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def rescale_gradients(self, scale: float):
 """ Rescales gradient arrays of executors by scale. """

        for exe in self.executors:
            for arr in exe.grad_arrays:
                if arr is None:
                    continue
                arr *= scale