Start process worker for given method args and kwargs.

def _start(self):
        """Start process worker for given method args and kwargs."""
        error = None
        output = None

        try:
            output = self.func(*self.args, **self.kwargs)
        except Exception as err:
            error = err

        if not self._is_finished:
            self.sig_finished.emit(self, output, error)
        self._is_finished = True