How to use the qcelemental.util.which_import function in qcelemental

"berny": which_import("berny", return_bool=True),
    "mdi": which_import("mdi", return_bool=True),
    "molpro": is_program_new_enough("molpro", "2018.1"),
    "mopac": is_program_new_enough("mopac", "2016"),
    "mp2d": which("mp2d", return_bool=True),
    "nwchem": which("nwchem", return_bool=True),
    "psi4": is_program_new_enough("psi4", "1.2"),
    "psi4_runqcsk": is_program_new_enough("psi4", "1.4a2.dev160"),
    "qcdb": which_import("qcdb", return_bool=True),
    "qchem": is_program_new_enough("qchem", "5.2"),
    "rdkit": which_import("rdkit", return_bool=True),
    "terachem": which("terachem", return_bool=True),
    "torchani": is_program_new_enough("torchani", "0.9"),
    "turbomole": which("define", return_bool=True),
}
_programs["openmm"] = _programs["rdkit"] and which_import(".openmm", package="simtk", return_bool=True)


def has_program(name):
    if name in _programs:
        return _programs[name]
    else:
        raise KeyError(f"Program {name} not registered with QCEngine testing.")


_using_cache = {}


def using(program):

    if program not in _using_cache:
        import_message = f"Not detecting module {program}. Install package if necessary to enable tests."

qcng.register_program(engine)

    yield engine

    qcng.unregister_program(engine.name)


# Figure out what is imported
_programs = {
    "cfour": which("xcfour", return_bool=True),
    "dftd3": which("dftd3", return_bool=True),
    "dftd3_321": is_program_new_enough("dftd3", "3.2.1"),
    "entos": is_program_new_enough("entos", "0.7.1"),
    "gamess": which("rungms", return_bool=True),
    "gcp": which("gcp", return_bool=True),
    "geometric": which_import("geometric", return_bool=True),
    "berny": which_import("berny", return_bool=True),
    "mdi": which_import("mdi", return_bool=True),
    "molpro": is_program_new_enough("molpro", "2018.1"),
    "mopac": is_program_new_enough("mopac", "2016"),
    "mp2d": which("mp2d", return_bool=True),
    "nwchem": which("nwchem", return_bool=True),
    "psi4": is_program_new_enough("psi4", "1.2"),
    "psi4_runqcsk": is_program_new_enough("psi4", "1.4a2.dev160"),
    "qcdb": which_import("qcdb", return_bool=True),
    "qchem": is_program_new_enough("qchem", "5.2"),
    "rdkit": which_import("rdkit", return_bool=True),
    "terachem": which("terachem", return_bool=True),
    "torchani": is_program_new_enough("torchani", "0.9"),
    "turbomole": which("define", return_bool=True),
}
_programs["openmm"] = _programs["rdkit"] and which_import(".openmm", package="simtk", return_bool=True)

If raise_error is True and psi4 is missing, the error message is raised.

        """
        psithon = which("psi4", return_bool=True)
        psiapi = which_import("psi4", return_bool=True)

        if psithon and not psiapi:
            with popen([which("psi4"), "--module"]) as exc:
                exc["proc"].wait(timeout=30)
            if "module does not exist" in exc["stderr"]:
                pass  # --module argument only in Psi4 DDD branch
            else:
                sys.path.append(exc["stdout"].split()[-1])

        if psiapi and not psithon:
            psiimport = str(Path(which_import("psi4")).parent.parent)
            env = os.environ.copy()
            env["PYTHONPATH"] = psiimport
            with popen(["python", "-c", "import psi4; print(psi4.executable[:-5])"], popen_kwargs={"env": env}) as exc:
                exc["proc"].wait(timeout=30)
            os.environ["PATH"] += os.pathsep + exc["stdout"].split()[-1]

        if psithon or psiapi:
            return True

        return which(
            "psi4",
            return_bool=True,
            raise_error=raise_error,
            raise_msg="Please install via `conda install psi4 -c psi4`. Check it's in your PATH with `which psi4`.",
        )

Parameters
        ----------
        raise_error: bool
            Passed on to control negative return between False and ModuleNotFoundError raised.

        Returns
        -------
        bool
            If psi4 (psithon or psiapi) is found, returns True.
            If raise_error is False and psi4 is missing, returns False.
            If raise_error is True and psi4 is missing, the error message is raised.

        """
        psithon = which("psi4", return_bool=True)
        psiapi = which_import("psi4", return_bool=True)

        if psithon and not psiapi:
            with popen([which("psi4"), "--module"]) as exc:
                exc["proc"].wait(timeout=30)
            if "module does not exist" in exc["stderr"]:
                pass  # --module argument only in Psi4 DDD branch
            else:
                sys.path.append(exc["stdout"].split()[-1])

        if psiapi and not psithon:
            psiimport = str(Path(which_import("psi4")).parent.parent)
            env = os.environ.copy()
            env["PYTHONPATH"] = psiimport
            with popen(["python", "-c", "import psi4; print(psi4.executable[:-5])"], popen_kwargs={"env": env}) as exc:
                exc["proc"].wait(timeout=30)
            os.environ["PATH"] += os.pathsep + exc["stdout"].split()[-1]

_addons_ = {
    "ambit": _CMake_to_Py_boolean("@ENABLE_ambit@"),
    "chemps2": _CMake_to_Py_boolean("@ENABLE_CheMPS2@"),
    "dkh": _CMake_to_Py_boolean("@ENABLE_dkh@"),
    "libefp": which_import("pylibefp", return_bool=True),
    "erd": _CMake_to_Py_boolean("@ENABLE_erd@"),
    "gdma": _CMake_to_Py_boolean("@ENABLE_gdma@"),
    "pcmsolver": _CMake_to_Py_boolean("@ENABLE_PCMSolver@"),
    "cppe": _CMake_to_Py_boolean("@ENABLE_cppe@"),
    "simint": _CMake_to_Py_boolean("@ENABLE_simint@"),
    "dftd3": psi4_which("dftd3", return_bool=True),
    "cfour": psi4_which("xcfour", return_bool=True),
    "mrcc": psi4_which("dmrcc", return_bool=True),
    "gcp": psi4_which("gcp", return_bool=True),
    "v2rdm_casscf": which_import("v2rdm_casscf", return_bool=True),
    "gpu_dfcc": which_import("gpu_dfcc", return_bool=True),
    "forte": which_import("forte", return_bool=True),
    "snsmp2": which_import("snsmp2", return_bool=True),
    "resp": which_import("resp", return_bool=True),
}


def addons(request=None):
    """Returns boolean of whether Add-On *request* is available to Psi4,
    either compiled in or searchable in $PSIPATH:$PATH, as relevant. If
    *request* not passed, returns list of available Add-Ons.

    """
    if request is None:
        return sorted([k for k, v in _addons_.items() if v])
    return _addons_[request.lower()]

def show(self, ngl_kwargs: Optional[Dict[str, Any]] = None) -> "nglview.NGLWidget":  # type: ignore
        """Creates a 3D representation of a moleucle that can be manipulated in Jupyter Notebooks and exported as
        images (`.png`).

        Parameters
        ----------
        ngl_kwargs : Optional[Dict[str, Any]], optional
            Addition nglview NGLWidget kwargs

        Returns
        -------
        nglview.NGLWidget
            A nglview view of the molecule

        """
        if not which_import("nglview", return_bool=True):
            raise ModuleNotFoundError(
                f"Python module nglwview not found. Solve by installing it: `conda install -c conda-forge nglview`"
            )  # pragma: no cover

        import nglview as nv  # type: ignore

        if ngl_kwargs is None:
            ngl_kwargs = {}

        structure = nv.TextStructure(self.to_string("nglview-sdf"), ext="sdf")
        widget = nv.NGLWidget(structure, **ngl_kwargs)
        return widget

def found(self, raise_error: bool = False) -> bool:
        return which_import(
            "geometric",
            return_bool=True,
            raise_error=raise_error,
            raise_msg="Please install via `conda install geometric -c conda-forge`.",
        )

_addons_ = {
    "ambit": _CMake_to_Py_boolean("@ENABLE_ambit@"),
    "chemps2": _CMake_to_Py_boolean("@ENABLE_CheMPS2@"),
    "dkh": _CMake_to_Py_boolean("@ENABLE_dkh@"),
    "libefp": which_import("pylibefp", return_bool=True),
    "erd": _CMake_to_Py_boolean("@ENABLE_erd@"),
    "gdma": _CMake_to_Py_boolean("@ENABLE_gdma@"),
    "pcmsolver": _CMake_to_Py_boolean("@ENABLE_PCMSolver@"),
    "cppe": _CMake_to_Py_boolean("@ENABLE_cppe@"),
    "simint": _CMake_to_Py_boolean("@ENABLE_simint@"),
    "dftd3": psi4_which("dftd3", return_bool=True),
    "cfour": psi4_which("xcfour", return_bool=True),
    "mrcc": psi4_which("dmrcc", return_bool=True),
    "gcp": psi4_which("gcp", return_bool=True),
    "v2rdm_casscf": which_import("v2rdm_casscf", return_bool=True),
    "gpu_dfcc": which_import("gpu_dfcc", return_bool=True),
    "forte": which_import("forte", return_bool=True),
    "snsmp2": which_import("snsmp2", return_bool=True),
    "resp": which_import("resp", return_bool=True),
}


def addons(request=None):
    """Returns boolean of whether Add-On *request* is available to Psi4,
    either compiled in or searchable in $PSIPATH:$PATH, as relevant. If
    *request* not passed, returns list of available Add-Ons.

    """
    if request is None:
        return sorted([k for k, v in _addons_.items() if v])
    return _addons_[request.lower()]

def found(raise_error: bool = False) -> bool:
        return which_import(
            "torchani",
            return_bool=True,
            raise_error=raise_error,
            raise_msg="Please install via `pip install torchani`.",
        )