According to http://bugs.alpinelinux.org/issues/5264 its known, that find_library is broken with python3 on Alpine.

However, with python2 it works on pure alpine:3.3,

$ docker run --rm -ti alpine:3.3 sh -c "apk add --no-cache file python && python -c 'from ctypes.util import find_library;print find_library(\"c\")'"
...
libc.musl-x86_64.so.1

but not on python:2-alpine,

$ docker run --rm -ti --entrypoint sh python:2-alpine -c "python -c 'from ctypes.util import find_library;print(find_library(\"c\"))'"
None

so python:2-alpine seems to break something in addition to the general alpine issue, which renders even version 2 broken. Maybe the find_library issue could also be worked around by python image in general.