Improved validation Dockerfile

validation/Dockerfile

-ARG VERSION_PYTHON="3.7"
+ARG VERSION_PYTHON="3.9"
 ARG VERSION_BASE_IMAGE="python:${VERSION_PYTHON}-alpine3.16"
 FROM ${VERSION_BASE_IMAGE}
 # We need to declare ARGs again which were declared before the build stage
@@ -131,11 +131,14 @@ RUN set -e pipefail; \
     apk del curl
 
 
-# for development
-#RUN set -e pipefail; \
-#    apk add bash emacs gcc build-base; \
-#    /usr/local/bin/python -m pip install pylint black; \
-#    apk del gcc build-base
+# switch to development version via build-arg
+ARG ADD_DEV
+RUN set -e pipefail; \
+    if test xYES == x`echo ${ADD_DEV} | tr '[:lower:]' '[:upper:]'`; then \
+      apk add bash emacs gcc build-base; \
+      /usr/local/bin/python -m pip install pylint black; \
+      apk del gcc build-base; \
+    fi
 
 ## Add a dedicated user for mmCIF file validation
 ## MMCIF_USER_ID can be used to avoid file permission issues in development.