Post install script after installing a wheel

Using from setuptools.command.install import install, I can easily run a custom post-install script if I run python setup.py install. This is fairly trivial to do.

Currently, the script does nothing but print some text but I want it to deal with system changes that need to happen when a new package is installed -- for example, back up the database that the package is using.

I want to generate the a Python wheel for my package and then copy that and install it on a a set of deployment machines. However, my custom install script is no longer run on the deployment machine.

What am I doing wrong? Is that even possible?

Solution 1:

Do not mix package installation and system deployment

Installation of Python packages (using any sort of packaging tools or formats) shall be focused on making that package usable from Python code.

Deployment, what might include database modifications etc. is definitely out of scope and shall be handled by other tools like fab, salt-stack etc.

The fact, that something seems fairly trivial does not mean, one shall do it.

The risk is, you will make your package installation difficult to reuse, as it will be spoiled by others things, which are not related to pure package installation.

The option to hook into installation process and modify environment is by some people even considered flaw in design, causing big mess in Python packaging situation - see Armin Roacher in Python Packaging: Hate, Hate, Hate Everywhere, chapter "PTH: The failed Design that enabled it all"

Solution 2:

PEP 427 which specifies the wheel package format does not leave any provisions for custom pre or post installation scripts.

Therefore running a custom script is not possible during wheel package installation.

You'll have to add the custom script to a place in your package where you expect the developer to execute first.