Should we gitignore the .python-version file?

While being too specific, you can still version that file (meaning: not include it in the default .gitignore), as :

• it will be used only by pyenv
• it is a good addition to the README, in order to illustrate what version of python is recommended for the specific project,
• it can be overridden easily (if you are using pyenv), or simply ignored (if you don't have pyenv).

As the article "How to manage multiple Python versions and virtual environments " states:

When setting up a new project that is to use Python 3.6.4 then pyenv local 3.6.4 would be ran in its root directory.
This would both set the version, and create a .python-version file, so that other contributors’ machines would pick it up.

But:

pyenv looks in four places to decide which version of Python to use, in priority order:

1. The PYENV_VERSION environment variable (if specified).
   You can use the pyenv shell command to set this environment variable in your current shell session.
2. The application-specific .python-version file in the current directory (if present).
   You can modify the current directory's .python-version file with the pyenv local command.
3. The first .python-version file found (if any) by searching each parent directory, until reaching the root of your filesystem.
4. The global version file. You can modify this file using the pyenv global command.
   If the global version file is not present, pyenv assumes you want to use the "system" Python. (In other words, whatever version would run if pyenv weren't in your PATH.)

The reason why .python-version should be gitignored is because its version is too specific. Tiny versions of Python (e.g. 2.7.1 vs 2.7.2) are generally compatible with each other, so you don't want to lock down to a specific tiny version. Furthermore, many Python apps or libraries should work with a range of Python versions, not just a specific one. Using .python-version indicates that you want other developers to use an exact, specific Python version, which is usually not a good idea.

If you want to indicate the minimum Python version needed, or otherwise a version range, then I believe documenting that in a README is a more appropriate solution.

It can also be a bit problematic when using python virtual environments, as people may want to use virtual environment names different than 3.7.2/envs/myvenv.