use extpython-python3.9

Dockerfile

@@ -16,7 +16,12 @@ RUN cd /tmp/code && \
 FROM ubuntu:focal AS app
 
 RUN apt-get update && \
-    apt-get install -y python3-pip
+    apt-get install -y wget gnupg && \
+    wget -qO- http://artifact.scc.net.davepedu.com/repo/apt/extpython/dists/focal/install | bash -x /dev/stdin && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y extpython-python3.9 libmagic1 ffmpeg && \
+    rm -rf /var/lib/apt/lists/*
+
+ENV PATH=/opt/extpython/3.9/bin/:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
 
 ADD . /tmp/code/
 COPY --from=frontend /tmp/code/styles/dist/style.css /tmp/code/styles/dist/style.css