expanduser path, PEP8

[scivision]

In general we use os.path.expanduser() wherever a user passes in a path to allow ~ to be used. This allows avoiding scenarios where users on laptop vs. HPC have to do the following:

• Windows laptop: c:\users\joe\data
• Linux HPC: /home/joe/data

where this PR allows them to simply use ~/data.

Also added Python 2 compatible type hint

Imports should almost always be at top of file, and we try to avoid "from x import y" to avoid namespace clashes. There is no advantage to hiding stdlib imports within functions in particular.

Type of change

• Bug fix (non-breaking change which fixes an issue)

[jklenzing]

Thanks @scivision. From looking into PEP484, it looks like the type hint should be employed since path=None is agnostic about the ultimate expected type. Is that right? Or am I missing something else?

[scivision]

I employ type hinting at every function declaration, universally in all programs.
Also within the function if necessary or for clarity.
When I do PRs I throw in type hints around the area I'm modifying, to help ensure I'm not breaking something.

I would say more than 10% of the bugs I find are from type hinting, it catches corner cases you wouldn't think of.

[scivision]

This page has notes about using type hinting in Python 2. Mypy is one of the most popular type hint checkers
https://mypy.readthedocs.io/en/latest/python2.html

[scivision]

I enforce PEP8 and type hints such that I cannot git commit until those pass (I can manually override, for example when working on someone else's project).

https://www.scivision.dev/git-commit-precheck-pep8/

A git pre-commit hook, itself written in Python https://github.com/scivision/gitMC/blob/master/pre-commit.py