Splitting 3 database3.py classes into 3 files

[john-science]

Description

The old database3.py file had 3 classes and several functions in it. But a better standard in Python is "1 class = 1 file" for big, meaty classes like this.

Also, I was not sure it was obvious to people what all was in this file.

Since the default GitHub diff for this PR is so large, I tried to keep my commits atomic, so you could see what all was being done more easily. So, I would suggest looking at the commits, and not the diff. Though, to help, here is a brief synopsis of the changes in this PR:

• db/database3.py:Database3 → no change
• db/database3.py:DatabaseInterface→ db/databaseInterface.py:DatabaseInterface
• db/database3.py:Layout → db/layout.py:Layout
• bookkeeping/tests/test_databaseInterface.py → bookkeeping/db/tests/test_databaseInterface.py

I also updated the major docstrings for db/database3.py, db/init.py, and Layout` to be up-to-date.

---

Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[keckler]

Just a note to any users, this changes where you need to import the databaseInterface from, if you import it directly.

[john-science]

Just a note to any users, this changes where you need to import the databaseInterface from, if you import it directly.

Just to be transparent: of course I reviewed every usage of DatabaseInterface in every repository that TerraPower has, and this does not break a single import or repo.

(It appears that since DatabaseInterface is a default Interface added to every ARMI run, no one imports it directly. )

[keckler]

Yeah, probably most people pull up that interface via getInterface(name="database"), because like you said it is always generated in a run.

I think its a good change. Just highlighting the API change.

[opotowsky]

Wow, great work! I found one downstream import of DatabaseInterface, but that doesn't block this in any way.

I didn't look hard at the tests or much of the code since it was just being moved around, but I did follow your commits as suggested so I did see the changes you made.

I think it looks really good.

[john-science]

Thanks for the save @opotowsky !