keras/src/callbacks/progbar_logger.py/ProgbarLogger/_update_progbar
class ProgbarLogger:    def _update_progbar(self, batch, logs=None):
        """Updates the progbar."""
        logs = logs or {}
        self._maybe_init_progbar()
        self.seen = batch + 1  # One-indexed.

        if self.verbose == 1:
            self.progbar.update(self.seen, list(logs.items()), finalize=False)