[abhinyaay]

Description

Omitted is a singleton enforced by SingletonMeta.__call__, but copy.copy, copy.deepcopy and pickle build new instances through cls.__new__(cls), bypassing the metaclass. Since Omitted defined no __reduce__ or copy hooks, a copied or unpickled sentinel compared unequal to the original:

import copy, pickle
from unihttp.omitted import Omitted

o = Omitted()
copy.copy(o) is o                    # was False
copy.deepcopy(o) == o                # was False
pickle.loads(pickle.dumps(o)) == o   # was False

This silently broke equality for any object with an Omitted-valued field once it round-tripped through deepcopy/pickle (Celery, multiprocessing, caches, dataclasses.asdict, ...), even though the objects looked identical via repr.

The fix keeps the singleton invariant across all three paths so Omitted always resolves back to the one instance:

• __copy__ / __deepcopy__ return self
• __reduce__ returns (type(self), ()), so unpickling routes back through SingletonMeta

With the singleton preserved, identity-based equality holds automatically, so no __eq__/__hash__ change is needed. The serializers keep working unchanged since they rely on isinstance.

Reported downstream in K1rL3s/maxo#241.

Testing

uv run pytest --cov src on Python 3.13: 414 passed, 4 skipped, 100% coverage. just lint (ruff check + format) and just static-analysis (mypy strict) both clean.

Type of change

• Bug fix (a non-breaking change that resolves an issue)

Checklist

• My code adheres to the style guidelines of this project (just lint shows no errors)
• I have conducted a self-review of my own code
• My changes do not generate any new warnings
• I have added tests to validate the effectiveness of my fix or the functionality of my new feature
• I have ensured that static analysis tests are passing by running just static-analysis

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a45033d) to head (fa59258).
⚠️ Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #17   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           33        33           
  Lines         1328      1334    +6     
=========================================
+ Hits          1328      1334    +6     

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