I'm developing an application using Python 3. What is the best practice to use third party libraries for development process and end-user distribution? Note that I'm working within these constraints:
There are no best practices, but there are a few different tracks people follow. With regard to commercial product distribution there are the following:
Manage Your Own Package Server
With regard to your development process, it is typical to either have your dev boxes update from a local package server. That allows you to "freeze" the dependency list (i.e. just stop getting upstream updates) so that everyone is on the same version. You can update at particular times and have the developers update as well, keeping everyone in lockstep.
For customer installs you usually write an install script. You can collect all the packages and install your libs, as well as the other at the same time. There can be issues with trying to install a new Python, or even any standard library because the customer may already depend on a different version. Usually you can install in a sandbox to separate your packages from the systems packages. This is more of a problem on Linux than Windows.
Toolchain
The other option is to create a toolchain for each supported OS. A toolchain is all the dependencies (up to, but not including base OS libs like glibc). This toolchain gets packaged up and distributed for both developers AND customers. Best practice for a toolchain is:
.../bin directories to prevent accidental usage. (ie. on Linux you can install under .../libexec. /opt is also used although personally I detest it.)lib/python/site-packages so you don't have to use PYTHONPATH..py files for the executables so the install script can relocate them appropriately.