Import slayer

[loriab]

Description

So in the course of working on DDD/pydantic, a fix I needed triggered the dreaded "circular import" error, which anyone who's tried to alter the driver's fragile import structure has probably seen, too. Being sick of this, I located https://medium.com/brexeng/avoiding-circular-imports-in-python-7c35ec8145ed with advice to do from .driver import energy, not from psi4.driver.driver import energy. So that's the first pass on the driver imports. This fixes my circular import problem and makes it easier to find others.

Since all the imports are churned anyways, I set up isort (that is, you can run isort on the repo, not that it's enforced on the repo). This is a utility (https://pycqa.github.io/isort/index.html) that sorts all the imports at the top of the file into stdlib, third_party, and first_party blocks and then alphabetizes the imports within. It also effectively tests the fragility of the import structure by jumbling them all into alphabetical order. Attempts in past years to run isort led to circular imports and a retreat. This time I was able to fix the single one that came about.

Third pass is that I ran autoflake on the driver to remove unused stdlib imports. It also removed some pass on empty fns that weren't needed because the docstring suffices for the syntax.

User notes

• the import structure has changed. you might need to add standard library imports to your input files if you use them (e.g., import math before math.pi) that previously were preloaded by psi4.

Dev notes & details

• switched import style to relative imports, ran isort, ran autoflake
• actual material changes:
  • stop importing molutil into sapt_proc. this is the main one that allows killing off the embarrassing temp_circular_import_blocker fn. https://github.com/psi4/psi4/compare/master...loriab:psi4:import_slayer?expand=1#diff-f3e93ffa6125dd1f79abad7630bbf259bb1daeee89e983d2889b68af6038875aL35
  • delay loading fisapt_proc until runtime in sapt_util. this releases the main circular import in procrouting. https://github.com/psi4/psi4/compare/master...loriab:psi4:import_slayer?expand=1#diff-b3bc4df41c2c04c815d7a8a9b374c88759487db4a68e9dc962785dae8cb4b73cR268
  • delay loading driver_findif in empirical_dispersion. https://github.com/psi4/psi4/compare/master...loriab:psi4:import_slayer?expand=1#diff-6c949ad06bfcc0f8d646a54c79a427c47e008cbdae82ca148b0f0af1e1319a63R379
  • kill off circular_import blocker from python_helpers and molutil https://github.com/psi4/psi4/compare/master...loriab:psi4:import_slayer?expand=1#diff-f1bd68ebb5a84a2a1bfea1cce073adda3b39a3146012026cb7841280ef8ca25dL658

Checklist

• tests added for any new features
• full tests pass

Status

• Ready for review
• Ready for merge

[JonathonMisiewicz]

Rubber-stamped.