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

def get_version(self) -> str:
        self.found(raise_error=True)

        which_prog = which('nwchem')
        if which_prog not in self.version_cache:
            success, output = execute([which_prog, "v.nw"], {"v.nw": ""})

            if success:
                for line in output["stdout"].splitlines():
                    if 'nwchem branch' in line:
                        branch = line.strip().split()[-1]
                    if 'nwchem revision' in line:
                        revision = line.strip().split()[-1]
                self.version_cache[which_prog] = safe_version(branch + '+' + revision)

        return self.version_cache[which_prog]

def get_version(self) -> str:
        self.found(raise_error=True)

        which_prog = which("rungms")
        if which_prog not in self.version_cache:
            success, output = execute([which_prog, "v.inp"], {"v.inp": ""})

            if success:
                for line in output["stdout"].splitlines():
                    if "GAMESS VERSION" in line:
                        branch = " ".join(line.strip(" *\t").split()[3:])
                self.version_cache[which_prog] = safe_version(branch)

        return self.version_cache[which_prog]

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]

        if psithon or psiapi:
            return True

def get_version(self) -> str:
        self.found(raise_error=True)

        which_prog = which("terachem")
        if which_prog not in self.version_cache:
            with popen([which_prog, "--version"]) as exc:
                exc["proc"].wait(timeout=5)
            mobj = re.search(NUMBER, exc["stdout"], re.VERBOSE)
            version = mobj.group(0)
            self.version_cache[which_prog] = safe_version(version)

        return self.version_cache[which_prog]

def get_version(self) -> str:
        self.found(raise_error=True)

        # Get the node configuration
        config = get_config()

        # Run NWChem
        which_prog = which("nwchem")
        if config.use_mpiexec:
            command = create_mpi_invocation(which_prog, config)
        else:
            command = [which_prog]
        command.append("v.nw")

        if which_prog not in self.version_cache:
            success, output = execute(command, {"v.nw": ""}, scratch_directory=config.scratch_directory)

            if success:
                for line in output["stdout"].splitlines():
                    if "nwchem branch" in line:
                        branch = line.strip().split()[-1]
                    if "nwchem revision" in line:
                        revision = line.strip().split()[-1]
                self.version_cache[which_prog] = safe_version(branch + "+" + revision)

def get_version(self) -> str:
        self.found(raise_error=True)

        which_prog = which("mp2d")
        if which_prog not in self.version_cache:
            # Note: anything below v1.1 will return an input error message here. but that's fine as version compare evals to False.
            command = [which_prog, "--version"]
            import subprocess

            proc = subprocess.run(command, stdout=subprocess.PIPE)
            self.version_cache[which_prog] = safe_version(proc.stdout.decode("utf-8").strip())

        return self.version_cache[which_prog]

def found(self, raise_error: bool = False) -> bool:
        return which(
            "entos", return_bool=True, raise_error=raise_error, raise_msg="Please install via https://www.entos.info/"
        )

def found(raise_error: bool = False) -> bool:
        return which(
            "xcfour", return_bool=True, raise_error=raise_error, raise_msg="Please install via http://cfour.de/"
        )

"""Whether NWChem harness is ready for operation, with both the QC program and any particular dependencies found.

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

        Returns
        -------
        bool
            If both nwchem and its harness dependency networkx are found, returns True.
            If raise_error is False and nwchem or networkx are missing, returns False.
            If raise_error is True and nwchem or networkx are missing, the error message for the first missing one is raised.

        """
        qc = which(
            "nwchem",
            return_bool=True,
            raise_error=raise_error,
            raise_msg="Please install via http://www.nwchem-sw.org/index.php/Download",
        )

        dep = which_import(
            "networkx",
            return_bool=True,
            raise_error=raise_error,
            raise_msg="For NWChem harness, please install via `conda install networkx -c conda-forge`.",
        )

        return qc and dep

def found(raise_error: bool = False) -> bool:
        return which(
            "mp2d",
            return_bool=True,
            raise_error=raise_error,
            raise_msg="Please install via `conda install mp2d -c psi4`",
        )