How to use the qcengine.programs.util.PreservingDict function in qcengine

def harvest_outfile_pass(outtext):
    """Function to read NWChem output file *outtext* and parse important
    quantum chemical information from it in

    """
    psivar = PreservingDict()
    psivar_coord = None
    psivar_grad = None
    version = ""
    error = ""  # TODO (wardlt): The error string is never used.

    NUMBER = r"(?x:" + regex.NUMBER + ")"
    # fmt: off

    # Process version
    mobj = re.search(
        r'^\s+' + r'Northwest Computational Chemistry Package (NWChem)' + r'\s+' + r'(?:\d+.\d+)' + r'\s*$',
        outtext, re.MULTILINE)
    if mobj:
        logger.debug('matched version')
        version = mobj.group('version')

def parse_reference_energy(stdout: str):
    """Parse stdout and return the energy of the reference wavefunction."""
    energy_dict = PreservingDict()

    # Total energy from dscf or ridft
    total_energy_re = re.compile("total energy\s+=\s+([\d\-\.]+)")
    mobj = total_energy_re.search(stdout)
    total_energy = Decimal(mobj[1])

    # Check for DFT, default to HF
    energy_key = "HF TOTAL ENERGY"
    dft_mobj = re.search("density functional", stdout)
    if dft_mobj:
        energy_key = "DFT TOTAL ENERGY"
    energy_dict[energy_key] = total_energy

    # Take into account energies from ricc2 runs. They will be different
    # from the HF energy.
    current_energy = total_energy

def parse_ricc2(stdout: str):
    ricc2_dict = PreservingDict()

    # As CC2 starts from a MP2 guess that is also reported there may be
    # multiple matches for the following regex. Thats why we capture all
    # matches with 'findall'.
    matches = parse_decimal("Final (.+?) energy\s+:\s+", stdout, "findall")
    if len(matches) == 0:
        matches = parse_decimal("E(MP2)\s+:\s+", stdout, "search")

    ricc2_dict["CURRENT ENERGY"] = matches[-1][1]

    return ricc2_dict

def harvest_outfile_pass(outtext):
    """Function to read CFOUR output file *outtext* and parse important
    quantum chemical information from it in

    """
    psivar = PreservingDict()
    psivar_coord = None
    psivar_grad = None
    version = ""
    error = ""

    #    TODO: BCC
    #          CI
    #          QCISD(T)
    #          other ROHF tests
    #          vcc/ecc

    # fmt: off
    NUMBER = r'(?x:' + regex.NUMBER + ')'

    # Process version
    mobj = re.search(r'^\s*' + r'Version' + r'\s+' + r'(?P[\w.]+)' + r'\s*$',

def harvest_outfile_pass(outtext):
    """Function to read gamess output file *outtext* and parse important
    quantum chemical information from it in
    """
    qcvar = PreservingDict()
    qcvar_coord = None
    qcvar_grad = None

    NUMBER = r"(?x:" + regex.NUMBER + ")"

    # If calculation fail to converge
    mobj = re.search(r"^\s+" + r"(?:GAMESS TERMINATED ABNORMALLY)" + r"\s*$", outtext, re.MULTILINE)
    if mobj:
        logger.debug("GAMESS TERMINATED ABNORMALLY")

    # If calculation converged
    # fmt: off
    else:
        mobj = re.search(
            r'^\s+' + r'(?:            TOTAL ENERGY)' + r'\s+=\s*' + NUMBER + r's*$',
            outtext, re.MULTILINE)

def harvest(input_model, stdout, **outfiles):
    qcvars = PreservingDict()

    ref_energy_dict = parse_reference_energy(stdout)
    qcvars.update(ref_energy_dict)

    if "R I C C 2" in stdout:
        ricc2_dict = parse_ricc2(stdout)
        qcvars.update(ricc2_dict)

    gradient = None
    if "gradient" in outfiles:
        gradient = parse_gradient(outfiles["gradient"])

    hessian = None
    return qcvars, gradient, hessian