variable_mgr.py 文件源码

def preprocess_device_grads(self, device_grads):
    """Preprocess the device gradients prior to applying them.

    Args:
      device_grads: List of lists of (gradient, variable) tuples.
        device_grads[t][g] = (gradient, variable), where t is the index of the
        tower and g is the index of the gradient-variable pair.

    Returns: a tuple of (apply_gradients_devices, gradient_state).
      gradient_state is an opaque structure that should be passed to
      get_gradients_to_apply() and append_apply_gradients_ops() (in that order).
      apply_gradients_devices is a list of devices where the gradients will be
      applied with get_gradients_to_apply() and append_apply_gradients_ops().
    """
    del device_grads  # unused by this implementation
    assert False, 'Must be implemented in subclass'