Find the name (if any) that a subclass was registered under.
    We do this simply by iterating through the registry until we
    find it.

def _get_config_type(cla55: type) -> Optional[str]:
    """
    Find the name (if any) that a subclass was registered under.
    We do this simply by iterating through the registry until we
    find it.
    """
    # Special handling for pytorch RNN types:
    if cla55 == torch.nn.RNN:
        return "rnn"
    elif cla55 == torch.nn.LSTM:
        return "lstm"
    elif cla55 == torch.nn.GRU:
        return "gru"

    for subclass_dict in Registrable._registry.values():
        for name, subclass in subclass_dict.items():
            if subclass == cla55:
                return name

        # Special handling for initializer functions
            if hasattr(subclass, '_initializer_wrapper'):
                sif = subclass()._init_function
                if sif == cla55:
                    return sif.__name__.rstrip("_")

    return None