Function freezable_variable

tensorflow/python/keras/backend.py:1074–1120

A tensor-like object whose value can be updated only up until execution. After creating the freezable variable, you can update its value by calling `var.update_value(new_value)` (similar to a regular variable). Unlike an actual variable, the value used during execution is the current value

(value, shape=None, name=None)

def freezable_variable(value, shape=None, name=None):
  """A tensor-like object whose value can be updated only up until execution.

  After creating the freezable variable, you can update its value by calling
  `var.update_value(new_value)` (similar to a regular variable).
  Unlike an actual variable, the value used during execution is the current
  value at the time the execution function (`backend.function()`) was created.

  This is an internal API, expected to be temporary. It is used to implement a
  mutable `trainable` property for `BatchNormalization` layers, with a frozen
  value after model compilation.

  We don't use a plain variable in this case because we need the value used
  in a specific model to be frozen after `compile` has been called
  (e.g. GAN use case).

  Arguments:
    value: The initial value for the tensor-like object.
    shape: The shape for the tensor-like object (cannot be changed).
    name: The name for the tensor-like object.

  Returns:
    A tensor-like object with a static value that can be updated via
    `x.update_value(new_value)`, up until creating an execution function
    (afterwards the value is fixed).
  """
  graph = get_graph()
  with graph.as_default():
    x = array_ops.placeholder_with_default(
        value, shape=shape, name=name)
    x._initial_value = value
    x._current_value = value

    def update_value(new_value):
      x._current_value = new_value

    def get_value():
      return x._current_value

    x.update_value = update_value
    x.get_value = get_value

    global _FREEZABLE_VARS
    if graph not in _FREEZABLE_VARS:
      _FREEZABLE_VARS[graph] = object_identity.ObjectIdentityWeakSet()
    _FREEZABLE_VARS[graph].add(x)
  return x


@keras_export('keras.backend.shape')