PR type: bugfix

Related issue(s)/PRs: related to 1985

Summary

Proposed changes

The wrapper for config constants is implemented as an Enum, even though it's not really being used as an enumeration. More problematically, Enums don't work correctly when two members have the same value and result in an alias for the first entry. The PR 1985 has this issue since both LIKELIHOODS_POSITIVE_MINIMUM and JITTER have the value 1e-6.

As proposed by this PR, we simply stop making the wrapper an enum. This forces us to explicitly state the environment variable names alongside the default values, but this duplication is not necessarily a bad thing.

What alternatives have you considered?

We could use an external enum package such as aenum that does support duplicate entries, but this introduces an unnecessary package dependency to GPflow.

Minimal working example

# Buggy behaviour
class _Values(enum.Enum):
     POSITIVE_MINIMUM = 0.0
     LIKELIHOODS_POSITIVE_MINIMUM = 1e-6
     JITTER = 1e-6

print(_Values.JITTER)
<_Values.LIKELIHOODS_POSITIVE_MINIMUM: 1e-06>

Release notes

Fully backwards compatible: yes

PR checklist

• New features: code is well-documented
  • detailed docstrings (API documentation)
  • notebook examples (usage demonstration)
• The bug case / new feature is covered by unit tests
• Code has type annotations
• Build checks
  • I ran the black+isort formatter (make format)
  • I locally tested that the tests pass (make check-all)
• Release management
  • RELEASE.md updated with entry for this change
  • New contributors: I've added myself to CONTRIBUTORS.md