'Called at the start of an epoch.
# Arguments
epoch: integer, index of epoch.
logs: dictionary of logs.'

def on_epoch_begin(self, epoch, logs=None):

    logs = (logs or {})
    for callback in self.callbacks:
        callback.on_epoch_begin(epoch, logs)
    self._delta_t_batch = 0.0
    self._delta_ts_batch_begin = deque([], maxlen=self.queue_length)
    self._delta_ts_batch_end = deque([], maxlen=self.queue_length)
