Fix bug introduced in previous commit : dual link list wasn't append and remove wasn't implemented correctly. Removed debug code, enhanced variable names and comments.
#
# Dockerfile for wxPython3.0 running on python2.7
#
FROM python:2.7-stretch
RUN set -xe \
&& apt-get update \
&& apt-get install -y --no-install-recommends python-wxgtk3.0 python-matplotlib \
&& apt-get install -y --no-install-recommends python-xvfbwrapper xvfb \
&& apt-get clean