[roottest] Inherit python executable from main process in nbdiff.py

This makes sure that we're using the exact Python version in the
notebook tests that ROOT was built against.

Author: guitargeek

roottest/python/JupyROOT/nbdiff.py

@@ -7,17 +7,7 @@
 import tempfile
 
 nbExtension = ".ipynb"
-convCmdTmpl = (
-    "%s nbconvert "
-    "--to notebook "
-    "--ExecutePreprocessor.kernel_name=%s "
-    "--ExecutePreprocessor.enabled=True "
-    "--ExecutePreprocessor.timeout=3600 "
-    "--ExecutePreprocessor.startup_timeout=180 "
-    "%s "
-    "--output %s"
-)
-pythonInterpName = "python3"
+pythonInterpName = sys.executable
 
 rootKernelFileContent = (
     """{
@@ -154,23 +144,32 @@ def getInterpreterName():
     yes, return its name else return 'ipython'
     """
     ret = subprocess.call("type jupyter", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    return "jupyter" if ret == 0 else "i%s" % pythonInterpName
+    return "jupyter nbconvert" if ret == 0 else "nbconvert"
 
 
 def getKernelName(inNBName):
     with open(inNBName) as f:
         nbj = json.load(f)
     if nbj["metadata"]["kernelspec"]["language"] == "python":
-        return pythonInterpName
+        return "python3"
     else:  # we support only Python and C++
         return "root"
 
 
-def canReproduceNotebook(inNBName, kernelName, needsCompare):
+def canReproduceNotebook(inNBName, needsCompare):
     tmpDir = addEtcToEnvironment(os.path.dirname(inNBName))
     outNBName = inNBName.replace(nbExtension, "_out" + nbExtension)
     interpName = getInterpreterName()
-    convCmd = convCmdTmpl % (interpName, kernelName, inNBName, outNBName)
+    convCmd = (
+        "%s -m %s "
+        "--to notebook "
+        "--ExecutePreprocessor.kernel_name=%s "
+        "--ExecutePreprocessor.enabled=True "
+        "--ExecutePreprocessor.timeout=3600 "
+        "--ExecutePreprocessor.startup_timeout=180 "
+        "%s "
+        "--output %s" % (pythonInterpName, interpName, getKernelName(inNBName), inNBName, outNBName)
+    )
     exitStatus = os.system(convCmd)  # we use system to inherit the environment in os.environ
     shutil.rmtree(tmpDir)
     if needsCompare:
@@ -206,7 +205,5 @@ def isInputNotebookFileName(filename):
     except:
         raise ImportError("Cannot import jupyter")
 
-    kernelName = getKernelName(nbFileName)
-
-    retCode = canReproduceNotebook(nbFileName, kernelName, needsCompare)
+    retCode = canReproduceNotebook(nbFileName, needsCompare)
     sys.exit(retCode)