Returns the input names and tensor specs associated with callable or None.

model A model that is callable or contains a signatures attribute. If neither of these conditions are met, then None will be returned.
signature_name Optional name of signature to use. If not provided then either the default serving signature will be used (if model is not callable) or the model itself will be used (if the model is callable). If provided then model.signatures will be used regardless of whether the model is callable or not.
required True if signature_name is required to exist if provided.

Dict mapping input names to their associated tensor specs or None if no callable could be found.

ValueError If signature_name not found in model.signatures.