Python3

Ansible role to install Python 3 and its apt package dependencies, and to install pip3 and pip3 packages both for user and system-wide scope.

Variables

Use the pip_packages list to define your pip packages for each of your hosts or groups. Each item of this list is a dict with the following structure:

- name: <pip-package-name> # mandatory
 install_scope: "system" # optional, not defining it is the same as setting it to empty string
 install_args: "" # optional, pip install <args>
 deps_apt: [] # optional, list of apt packages that the pip module depends on

The pip packages defined in defaults will be merged with your list of pip packages. Note that the merge will not overwrite existing list items nor their properties (for example, { name: setuptools, install_scope: "system" } will not be affected if you define { name: setuptools } in your list).

Links and notes

• https://launchpad.net/~deadsnakes/+archive/ubuntu/ppa
• https://askubuntu.com/questions/1398568/installing-python-who-is-deadsnakes-and-why-should-i-trust-them

Other Ansible roles

• https://github.com/mdklatt/ansible-python3-role
• https://github.com/fubarhouse/ansible-role-python

Something as conceptually simply as listing all package dependencies

Turns out to be immensely complicated for pip packages. No simple solution yet. Maybe pipdeptree --packages <pip-package> does what we want?

• https://stackoverflow.com/questions/11147667/is-there-a-way-to-list-pip-dependencies-requirements
• https://www.activestate.com/resources/quick-reads/how-to-check-for-python-dependencies-with-popular-package-managers/
• https://pip.pypa.io/en/latest/topics/dependency-resolution/

Why we install pip packages as user, not root

I have moved away from installing pip and pip packages system-wide because that lead to really hard-to-overcome clashes between pip packages and apt packages, such as pycairo.

Attempting uninstall: pycairo
Found existing installation: pycairo 1.16.2
stderr: ERROR: Cannot uninstall 'pycairo'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall

What if we uninstall python3-cairo?

$ sudo apt remove python3-cairo
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
 fortune-mod fortunes-min gedit-common gir1.2-ayatanaappindicator3-0.1 gir1.2-gexiv2-0.10
 gir1.2-gtksource-3.0 libayatana-appindicator3-1 libayatana-indicator3-7 libgexiv2-2 libgspell-1-1
 libgspell-1-common libgtksourceview-3.0-1 libgtksourceview-3.0-common librecode0 python3-bs4
 python3-html5lib python3-lxml python3-olefile python3-pil python3-webencodings
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED
 gedit meld python3-cairo python3-cairo-dev python3-gi-cairo variety
0 to upgrade, 0 to newly install, 6 to remove and 21 not to upgrade.

No, it is a dependency of multiple other packages and would break too much stuff.

Options?

• simply power on by adding --ignore-installed to pip extra args, but that risks putting the entire system in an unmaintainable state
• would it help if we changed pip_user from root to {{ ansible_env.USER }}? (we don't really need it to be root...)
• if that does not help, then what?
• install more pip packages in their own virtualenvs, instead of like now?
• install python from source (a so-called private python installation), would that help?

Good commentary on this subject:

• https://stackoverflow.com/questions/49932759/pip-10-and-apt-how-to-avoid-cannot-uninstall-x-errors-for-distutils-packages
• https://stackoverflow.com/questions/53807511/pip-cannot-uninstall-package-it-is-a-distutils-installed-project/53807588#53807588