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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 error_handler(self, handler):
 """Setter for the error handler function. If the DLL is open, this function is a no-op, so it should be called prior to calling ``open()``. Args: self (JLink):
 the ``JLink`` instance handler (function):
 function to call on error messages Returns: ``None`` """

        if not self.opened():
            handler = handler or util.noop
            self._error_handler = enums.JLinkFunctions.LOG_PROTOTYPE(handler)
            self._dll.JLINKARM_SetErrorOutHandler(self._error_handler)