keras/src/layers/preprocessing/feature_space.py/FeatureSpace/_convert_input
class FeatureSpace:    def _convert_input(self, x):
        if not isinstance(x, (tf.Tensor, tf.SparseTensor, tf.RaggedTensor)):
            if not isinstance(x, (list, tuple, int, float)):
                x = backend.convert_to_numpy(x)
            x = tf.convert_to_tensor(x)
        return x