def process_mol_type(mol_type: str) -> str:
    """
    Convert potential mol_type strings into valid mol_type strings.

    Args:
        mol_type: Unprocessed mol type.

    Returns:
        'pybel' or 'rdkit'.
    """
    mol_type_new = mol_type.lower()
    if mol_type_new in {'pybel', 'babel', 'obabel', 'openbabel'}:
        return 'pybel'
    elif mol_type_new == 'rdkit':
        return 'rdkit'
    else:
        raise ValueError(f'Invalid molecule type "{mol_type}"')