Python package and virtual environment management can be a bit tricky. This post has some best and bad practices from a personal point of view.
Virtual environment findings
- Usevenv (
python3 -m venv) instead ofvirtualenv (virtualenv venv) when you don't need virtual environments with different python versions. venv is the python 3.3+ default one and we have not had the need for using the other one. You can get some feedback from here. However, if your virtual environments use different python versions, _venv_simply does not support it. - Try to never install anything that you could use in a python project outside of a virtualenv. Or
better; think twice before using
pip installoutside of a virtual environment in general. I promise you it will get messy in the future, specially if you use site packages. - Try not to use
--system-site-packagesuntil strictly needed. This can easily go wrong because of the point above; you end up having projects competing for different versions of packages and similar things. - For now we have only one reason to use
--system-site-packages, and it is to access apt-ed installed packages from the command-line directly. - Some packages can have special needs, like suggested for Tkinter. We will need to check this approach.
- regardless of the pip that you have installed globally. This is_a feature :-) ._Unluckily it means that because of the SSL fiasco of pip we cannot install packages in the virtual environment,
A peak in how virtual environment works
So, to create a virtual environment we just do python3 -m venv, which creates a virtual
environment inside a folder_venv_with the same python version that we have installed.
To activate the virtual env, cd to the project folder and use source venv/bin/activatein a Unix
system. Note that source is a Unix command, not a python one, and it just executes the contents
of the script in_venv/bin/activate_, which temporarily loads variables in our terminal. Some of
those variables that virtual environment sets replace the python executable, the pip executable,
and the directory where pip looks for packages, to directories inside the venv folder. So when we
execute python we execute the python inside the venv folder (try to do which python after you
performed source).
You can safely modify_/venv/bin/activate_ to do things when you execute source,for example this.
I will keep this post updated with new findings and practices. The next update will probably be how
to correctly access aptpackages.
Delete all python packages
If you screwed-up and want to delete all pip-installed python packages you can do[note]From here .[/note]:
pip3 freeze --local | grep -v "^-e" | xargs sudo pip3 uninstall -y
Fixing pip 9 in Mac
If you are using Python 3.5 or under and are in a Mac you will have the problem that you cannot install any package due some network error. This is because Mac's library is outdated and Pypi rejects it. Use the following to update pip[note] Fromhttps://github.com/pypa/pip/issues/5236#issuecomment-381678057 [/note]:
curl https://bootstrap.pypa.io/get-pip.py | python3