def get(identifier):
    """Retrieve a Keras activation function via an identifier."""
    if identifier is None:
        return linear
    if isinstance(identifier, dict):
        obj = serialization_lib.deserialize_keras_object(identifier)
    elif isinstance(identifier, str):
        obj = ALL_OBJECTS_DICT.get(identifier, None)
    else:
        obj = identifier
    if callable(obj):
        return obj
    raise ValueError(
        f"Could not interpret activation function identifier: {identifier}"
    )
Retrieve a Keras activation function via an identifier.
keras/src/activations/__init__.py