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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 step(self, thumb=False):
 """Executes a single step. Steps even if there is a breakpoint. Args: self (JLink):
 the ``JLink`` instance thumb (bool):
 boolean indicating if to step in thumb mode Returns: ``None`` Raises: JLinkException: on error """

        method = self._dll.JLINKARM_Step
        if thumb:
            method = self._dll.JLINKARM_StepComposite

        res = method()
        if res != 0:
            raise errors.JLinkException("Failed to step over instruction.")

        return None