Use alpine python base image

[richford]

We can reduce the size of the docker image by using the alpine python base image. From https://hub.docker.com/_/python/:

This image is based on the popular Alpine Linux project, available in the alpine official image. Alpine Linux is much smaller than most distribution base images (~5MB), and thus leads to much slimmer images in general.

This variant is highly recommended when final image size being as small as possible is desired. The main caveat to note is that it does use musl libc instead of glibc and friends, so certain software might run into issues depending on the depth of their libc requirements. However, most software doesn't have an issue with this, so this variant is usually a very safe choice. See this Hacker News comment thread for more discussion of the issues that might arise and some pro/con comparisons of using Alpine-based images.

To minimize image size, it's uncommon for additional related tools (such as git or bash) to be included in Alpine-based images. Using this image as a base, add the things you need in your own Dockerfile (see the alpine image description for examples of how to install packages if you are unfamiliar).

[richford]

But it turns out that installing numpy is difficult with the alpine python image. See

• apk add numpy is not working on python:2.7.11-alpine docker-library/python#112
• https://stackoverflow.com/questions/33421965/installing-numpy-on-docker-alpine

For now, it's probably better to stick with the general base image.