enhance 'eb' command to ensure that easybuild.main can be imported before settling on python* command to use

Author: boegel

.github/workflows/eb_command.yml

@@ -73,15 +73,15 @@ jobs:
           pymajver=$(python -c 'import sys; print(sys.version_info[0])')
           pymajminver=$(python -c 'import sys; print(".".join(str(x) for x in sys.version_info[:2]))')
           # check patterns in verbose output
-          for pattern in "^>> Considering .python.\.\.\." "^>> .python. version: ${pymajminver}\.[0-9]\+, which matches Python ${pymajver} version requirement" "^>> Selected Python command: python \(.*/bin/python\)" "^This is EasyBuild 4\.[0-9.]\+"; do
+          for pattern in "^>> Considering .python.\.\.\." "^>> .python. version: ${pymajminver}\.[0-9]\+, which matches Python ${pymajver} version requirement" "^>> 'python' is able to import 'easybuild.main', so retaining it" "^>> Selected Python command: python \(.*/bin/python\)" "^This is EasyBuild 4\.[0-9.]\+"; do
               echo "Looking for pattern \"${pattern}\" in eb_version.out..."
               grep "$pattern" eb_version.out
           done
           # also check when specifying Python command via $EB_PYTHON
           for eb_python in "python${pymajver}" "python${pymajminver}"; do
               export EB_PYTHON="${eb_python}"
               eb --version | tee eb_version.out 2>&1
-              for pattern in "^>> Considering .${eb_python}.\.\.\." "^>> .${eb_python}. version: ${pymajminver}\.[0-9]\+, which matches Python ${pymajver} version requirement" "^>> Selected Python command: ${eb_python} \(.*/bin/${eb_python}\)" "^This is EasyBuild 4\.[0-9.]\+"; do
+              for pattern in "^>> Considering .${eb_python}.\.\.\." "^>> .${eb_python}. version: ${pymajminver}\.[0-9]\+, which matches Python ${pymajver} version requirement" "^>> '${eb_python}' is able to import 'easybuild.main', so retaining it" "^>> Selected Python command: ${eb_python} \(.*/bin/${eb_python}\)" "^This is EasyBuild 4\.[0-9.]\+"; do
                   echo "Looking for pattern \"${pattern}\" in eb_version.out..."
                   grep "$pattern" eb_version.out
               done

eb

@@ -37,6 +37,7 @@
 REQ_MIN_PY2VER=6
 REQ_MIN_PY3VER=5
 
+EASYBUILD_MAIN='easybuild.main'
 
 function verbose() {
     if [ ! -z ${EB_VERBOSE} ]; then echo ">> $1"; fi
@@ -52,6 +53,8 @@ for python_cmd in ${EB_PYTHON} ${EB_INSTALLPYTHON} 'python' 'python3' 'python2';
 
     verbose "Considering '$python_cmd'..."
 
+    # check whether python* command being considered is available
+    # (using 'command -v', since 'which' implies an extra dependency)
     command -v $python_cmd &> /dev/null
     if [ $? -eq 0 ]; then
 
@@ -63,10 +66,25 @@ for python_cmd in ${EB_PYTHON} ${EB_INSTALLPYTHON} 'python' 'python3' 'python2';
         if [ $pyver_maj -eq 2 ] && [ $pyver_min -ge $REQ_MIN_PY2VER ]; then
             verbose "'$python_cmd' version: $pyver, which matches Python 2 version requirement (>= 2.$REQ_MIN_PY2VER)"
             PYTHON=$python_cmd
-            break
         elif [ $pyver_maj -eq 3 ] && [ $pyver_min -ge $REQ_MIN_PY3VER ]; then
             verbose "'$python_cmd' version: $pyver, which matches Python 3 version requirement (>= 3.$REQ_MIN_PY3VER)"
             PYTHON=$python_cmd
+        fi
+
+        if [ ! -z $PYTHON ]; then
+            # check whether easybuild.main is available for selected python command
+            $PYTHON -c "import $EASYBUILD_MAIN" 2> /dev/null
+            if [ $? -eq 0 ]; then
+                verbose "'$python_cmd' is able to import '$EASYBUILD_MAIN', so retaining it"
+            else
+                # if easybuild.main is not available, don't use this python command, keep searching...
+                verbose "'$python_cmd' is NOT able to import '$EASYBUILD_MAIN', so NOT retaining it"
+                unset PYTHON
+            fi
+        fi
+
+        # break out of for loop if we've found a valid python command
+        if [ ! -z $PYTHON ]; then
             break
         fi
     else
@@ -97,5 +115,5 @@ fi
 
 export EB_SCRIPT_PATH=$0
 
-verbose "$PYTHON -m easybuild.main `echo \"$@\"`"
-$PYTHON -m easybuild.main "$@"
+verbose "$PYTHON -m $EASYBUILD_MAIN `echo \"$@\"`"
+$PYTHON -m $EASYBUILD_MAIN "$@"