src/transformers/optimization_tf.py/GradientAccumulator/step
class GradientAccumulator:    def step(self):
        """Number of accumulated steps."""
        if self._accum_steps is None:
            self._accum_steps = tf.Variable(
                tf.constant(0, dtype=tf.int64),
                trainable=False,
                synchronization=tf.VariableSynchronization.ON_READ,
                aggregation=tf.VariableAggregation.ONLY_FIRST_REPLICA,
            )

        return self._accum_steps.value()