keras-team/keras · error · ValueError

A `Subtract` layer should be called on exactly 2 inputs. Rec

Error message

A `Subtract` layer should be called on exactly 2 inputs. Received: input_shape={input_shape}

What it means

Error "A `Subtract` layer should be called on exactly 2 inputs. Received: input_shape={input_shape}" thrown in keras-team/keras.

Source

Thrown at keras/src/layers/merging/subtract.py:37

    >>> y = keras.layers.Subtract()([x1, x2])

    Usage in a Keras model:

    >>> input1 = keras.layers.Input(shape=(16,))
    >>> x1 = keras.layers.Dense(8, activation='relu')(input1)
    >>> input2 = keras.layers.Input(shape=(32,))
    >>> x2 = keras.layers.Dense(8, activation='relu')(input2)
    >>> # equivalent to `subtracted = keras.layers.subtract([x1, x2])`
    >>> subtracted = keras.layers.Subtract()([x1, x2])
    >>> out = keras.layers.Dense(4)(subtracted)
    >>> model = keras.models.Model(inputs=[input1, input2], outputs=out)

    """

    def build(self, input_shape):
        super().build(input_shape)
        if len(input_shape) != 2:
            raise ValueError(
                "A `Subtract` layer should be called on exactly 2 inputs. "
                f"Received: input_shape={input_shape}"
            )

    def _merge_function(self, inputs):
        if len(inputs) != 2:
            raise ValueError(
                "A `Subtract` layer should be called on exactly 2 inputs. "
                f"Received: inputs={inputs}"
            )
        return ops.subtract(inputs[0], inputs[1])


@keras_export("keras.layers.subtract")
def subtract(inputs, **kwargs):
    """Functional interface to the `keras.layers.Subtract` layer.

    Args:

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/layers/merging/subtract.py:37 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of keras-team/keras@7a34a03db6 (2026-08-25). Data as JSON: /api/errors/c77dfc30a8cc5e97. Report an issue: GitHub.