performs on-loop-start actions like callbacks

        variables contains local namespace variables.

        Parameters
        ---------
        variables : dict of available variables

        Returns
        -------
        None

def _on_loop_start(self, variables):
        """
        performs on-loop-start actions like callbacks

        variables contains local namespace variables.

        Parameters
        ---------
        variables : dict of available variables

        Returns
        -------
        None
        """
        for callback in self.callbacks:
            if hasattr(callback, 'on_loop_start'):
                self.logs_[str(callback)].append(callback.on_loop_start(**variables))