Fixes #1253: Improved upgrade.sh to allow forcing Python2

docs/installation/upgrading.md

@@ -52,6 +52,13 @@ Once the new code is in place, run the upgrade script (which may need to be run
 # ./upgrade.sh
 ```
 
+!!! warning
+    The upgrade script will prefer Python3 and pip3 if both executables are available. To force it to use Python2 and pip, use the `-2` argument as below.
+
+```no-highlight
+# ./upgrade.sh -2
+```
+
 This script:
 
 * Installs or upgrades any new required Python packages

upgrade.sh

@@ -5,6 +5,25 @@
 # Once the script completes, remember to restart the WSGI service (e.g.
 # gunicorn or uWSGI).
 
+# Determine which version of Python/pip to use. Default to v3 (if available)
+# but allow the user to force v2.
+PYTHON="python3"
+PIP="pip3"
+type $PYTHON >/dev/null 2>&1 && type $PIP >/dev/null 2>&1 || PYTHON="python" PIP="pip"
+while getopts ":2" opt; do
+    case $opt in
+        2)
+            PYTHON="python"
+            PIP="pip"
+            echo "Forcing Python/pip v2"
+            ;;
+        \?)
+            echo "Invalid option: -$OPTARG" >&2
+            exit
+            ;;
+    esac
+done
+
 # Optionally use sudo if not already root, and always prompt for password
 # before running the command
 PREFIX="sudo -k "
@@ -20,12 +39,6 @@ COMMAND="${PREFIX}find . -name \"*.pyc\" -delete"
 echo "Cleaning up stale Python bytecode ($COMMAND)..."
 eval $COMMAND
 
-# Prefer python3/pip3
-PYTHON="python3"
-type $PYTHON >/dev/null 2>&1 || PYTHON="python"
-PIP="pip3"
-type $PIP >/dev/null 2>&1 || PIP="pip"
-
 # Install any new Python packages
 COMMAND="${PREFIX}${PIP} install -r requirements.txt --upgrade"
 echo "Updating required Python packages ($COMMAND)..."