Use sys.executable over explicit call to python (#451)

* Use sys.executable over explicit call to python which may not be available

* Update changelog.rst

---------

Co-authored-by: Lori A. Burns <[email protected]>

docs/source/changelog.rst

@@ -44,6 +44,7 @@ Enhancements
 
 Bug Fixes
 +++++++++
+- (:pr:`451`, :issue:`450`) Psi4 - Fixes bug in Psi4 detection when command `python` not available. @susilehtola, @topazus
 
 Misc.
 +++++

qcengine/programs/psi4.py

@@ -73,7 +73,7 @@ def found(raise_error: bool = False) -> bool:
                         psiapi = which_import("psi4", return_bool=True)
 
         if psiapi and not psithon:
-            with popen(["python", "-c", "import psi4; print(psi4.executable)"]) as exc:
+            with popen([sys.executable, "-c", "import psi4; print(psi4.executable)"]) as exc:
                 exc["proc"].wait(timeout=30)
             so, se, rc = exc["stdout"].strip(), exc["stderr"], exc["proc"].returncode
             error_msg = f" In particular, psi4 module found but unable to load psi4 command into PATH. stdout: {so}, stderr: {se}"