defined constants for LEFT and RIGHT

[JustinSGray]

Purpose

left and right would be better as module level constants, making the IDE more effective.

Type of change

Addition of constants

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

No new tests needed, but existing tests were updated to use the constants to verify functionality

Checklist

(note: not enforcing line number restriction on this codebase)

• I have run flake8 and black to make sure the code adheres to PEP-8 and is consistently formatted
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation

[ewu63]

Changes look okay. Longer term, I would like to change these (and all the OPT etc.) to enums, but that doesn't have to happen in this PR.

[ewu63]

We decided to get this in and make a release first, before making the (potentially backwards incompatible) changes.