Python 2 installation fails due to f-strings and type annotations

[adeadman]

Currently the project is listed on PyPI as supporting Python 2, but installation fails with a SyntaxError due to the use of f-strings such as in __internals.py#L102 and L388, and type annotations such as __internals.py#L128

How to reproduce: pip install python-pam

Expected result: The package successfully builds and installs to site-packages

The installation process does warn that Py2 support has been deprecated, and so the package is no longer being checked for correctness. In this case it might be worthwhile updating the package entry on PyPI to remove Python 2 as a supported environment. However, if support for Py2 should be maintained for as long as possible, the f-string could be replaced with a format call, and type annotations with the PEP-484 straddling type annotation syntax.