Keras
Keras 3 API documentation
Layers API
Core layers
InputSpec object

InputSpec object

source

InputSpec class 

keras.InputSpec(
    dtype=None,
    shape=None,
    ndim=None,
    max_ndim=None,
    min_ndim=None,
    axes=None,
    allow_last_axis_squeeze=False,
    name=None,
    optional=False,
)

Specifies the rank, dtype and shape of every input to a layer.

Layers can expose (if appropriate) an input_spec attribute: an instance of InputSpec, or a nested structure of InputSpec instances (one per input tensor). These objects enable the layer to run input compatibility checks for input structure, input rank, input shape, and input dtype for the first argument of Layer.__call__.

A None entry in a shape is compatible with any dimension.

Arguments

  • dtype: Expected dtype of the input.
  • shape: Shape tuple, expected shape of the input (may include None for dynamic axes). Includes the batch size.
  • ndim: Integer, expected rank of the input.
  • max_ndim: Integer, maximum rank of the input.
  • min_ndim: Integer, minimum rank of the input.
  • axes: Dictionary mapping integer axes to a specific dimension value.
  • allow_last_axis_squeeze: If True, allow inputs of rank N+1 as long as the last axis of the input is 1, as well as inputs of rank N-1 as long as the last axis of the spec is 1.
  • name: Expected key corresponding to this input when passing data as a dictionary.
  • optional: Boolean, whether the input is optional or not. An optional input can accept None values.

Example

class MyLayer(Layer):
    def __init__(self):
        super().__init__()
        # The layer will accept inputs with
        # shape (*, 28, 28) & (*, 28, 28, 1)
        # and raise an appropriate error message otherwise.
        self.input_spec = InputSpec(
            shape=(None, 28, 28, 1),
            allow_last_axis_squeeze=True)