Merge branch 'improvements' into 'main'

Make executables installed with pip available and make "main python" the default

Closes #3

See merge request divio/incubator/multi-python!5

Author: derlin

Dockerfile

@@ -71,7 +71,15 @@ RUN set -eux \
   ; fi \
   ; mkdir /pypy && tar -xf /pypy.tar.bz2 -C /pypy --strip-components=1
 
-ENV PATH="/pypy/bin:$PATH"
+# Make pypi available and ensure executables installed by pip are available
+# (pip uses the "User Scheme" in recent Debian/Ubuntu,
+# see https://packaging.python.org/en/latest/guides/installing-using-linux-tools/#debian-ubuntu)
+ENV PATH="$PATH:/pypy/bin:/home/tox/.local/bin"
+
+# Set the default python version
+RUN set -eux \
+  ; ln -f -s /usr/bin/python${PYTHON_MAIN_VERSION} /usr/bin/python \
+  ; ln -f -s /usr/bin/python${PYTHON_MAIN_VERSION} /usr/bin/python3
 
 # Create user (with sudo privileges) and app directory
 RUN set -eux \

README.md

@@ -11,6 +11,8 @@ The list of Python versions to install is passed as arguments (see `Dockerfile`)
 One Python version must be selected as "main" - it will be used to install `tox`.
 Along with "regular" Python versions, one pypy version will also be installed.
 
+The main python version is set as the default in the container (`python` and `python3`).
+
 **IMPORTANT**: Python versions must be available either in the official Ubuntu repositories or in
 the [deadsnakes PPA](https://launchpad.net/~deadsnakes/+archive/ubuntu/ppa). The PyPy version should
 be available at https://www.pypy.org/download.html.
@@ -29,3 +31,16 @@ so it is possible to run `sudo apt update && sudo apt install ...`.
 
 After updating the Python versions in the `Dockerfile`, ensure you also update `test/tox.ini` to
 reflect the change.
+
+## About pip
+
+As stated in https://packaging.python.org/en/latest/guides/installing-using-linux-tools/#debian-ubuntu:
+
+> Recent Debian/Ubuntu versions have modified pip to use the “User Scheme” by default,
+> which is a significant behavior change that can be surprising to some users.
+
+In other words, pip now installs libraries and executables in `$HOME/.local` (or `/home/tox/.local`
+in this image).
+
+This has no impact, except when running commands as `sudo`. Just keep in mind the `root` user
+doesn't have the same packages installed.