[jupyterhub] configurable python version, default to 3.8

jupyterhub/Dockerfile

@@ -9,6 +9,8 @@ RUN apt-get update && \
         curl && \
     apt-get clean
 
+ARG PYTHON_VERSION=3.8
+
 RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
     apt-get update && \
     apt-get install -y \
@@ -18,21 +20,21 @@ RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
         openjdk-11-jre-headless && \
     apt-get clean
 
-RUN python3.7 -m pip --no-cache-dir install \
+RUN python${PYTHON_VERSION} -m pip --no-cache-dir install \
         jupyterlab \
         jupyterhub \
         ipympl \
 	&& \
-    python3.7 -m jupyter labextension install \
+    python${PYTHON_VERSION} -m jupyter labextension install \
         @jupyter-widgets/jupyterlab-manager && \
-    python3.7 -m jupyter serverextension enable --sys-prefix --py jupyterlab && \
-    python3.7 -m jupyter labextension install \
+    python${PYTHON_VERSION} -m jupyter serverextension enable --sys-prefix --py jupyterlab && \
+    python${PYTHON_VERSION} -m jupyter labextension install \
         jupyter-webrtc \
         ipyvolume \
         jupyter-threejs
 
 RUN mkdir -p ~/.venv && \
-    python3.7 -m venv ~/.venv/robofish && \
+    python${PYTHON_VERSION} -m venv ~/.venv/robofish && \
     . ~/.venv/robofish/bin/activate && \
     pip --no-cache-dir install --upgrade pip==20.1.1 && \
     pip --no-cache-dir install --upgrade setuptools==49.1.0 && \