Install multiple pythons on CircleCI

.circleci/images/Dockerfile

@@ -1,7 +1,7 @@
 FROM ubuntu:latest
 
 # System setup
-RUN apt-get update && apt-get install -y python3-flake8 python3-pip python3-pil clang git openssh-client make-guile
+RUN apt-get update && apt-get install -y python3-flake8 python3-pip python3-pil clang git openssh-client build-essential libreadline-dev zlib1g-dev libssl-dev libbz2-dev libsqlite3-dev libffi-dev 
 
 # kitty deps
 RUN apt-get install -y libgl1-mesa-dev libxi-dev libxrandr-dev libxinerama-dev libxcursor-dev libxcb-xkb-dev libdbus-1-dev libxkbcommon-dev libharfbuzz-dev libpng-dev libfontconfig-dev libpython3-dev libxkbcommon-x11-dev python3-pygments
@@ -9,5 +9,10 @@ RUN apt-get install -y libgl1-mesa-dev libxi-dev libxrandr-dev libxinerama-dev l
 # Needed to build kitty docs
 RUN pip3 install sphinx
 
+# Install multiple pythons
+ADD install-python.py /tmp/install-python.py
+RUN python3 /tmp/install-python.py py3.5 https://www.python.org/ftp/python/3.5.6/Python-3.5.6.tar.xz
+RUN python3 /tmp/install-python.py py3.7 https://www.python.org/ftp/python/3.7.2/Python-3.7.2.tar.xz
+
 LABEL com.circleci.preserve-entrypoint=true
 ENTRYPOINT sleep 2h

.circleci/images/install-python.py

@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+# vim:fileencoding=utf-8
+# License: GPLv3 Copyright: 2019, Kovid Goyal <kovid at kovidgoyal.net>
+
+import io
+import os
+import shlex
+import shutil
+import subprocess
+import sys
+import tarfile
+from urllib.request import urlopen
+
+PY, URL = sys.argv[1], sys.argv[2]
+SRC = f'/usr/src/{PY}'
+
+os.chdir('/usr/src')
+before = frozenset(os.listdir('.'))
+
+
+def run(cmd):
+    cmd = shlex.split(cmd)
+    p = subprocess.Popen(cmd)
+    if p.wait() != 0:
+        raise SystemExit(p.returncode)
+
+
+with urlopen(URL) as f:
+    data = f.read()
+
+with tarfile.open(fileobj=io.BytesIO(data), mode='r:xz') as tf:
+    tf.extractall()
+after = frozenset(os.listdir('.'))
+src_dir = tuple(after - before)[0]
+os.rename(src_dir, SRC)
+os.chdir(SRC)
+run(f'./configure --prefix=/opt/{PY} --enable-shared --with-system-expat --with-system-ffi --without-ensurepip')
+run(f'make -j {os.cpu_count()}')
+run('make install')
+os.chdir('/')
+shutil.rmtree(SRC)