fix: make Number hashable so it works in sets and dict keys#20
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Defining __eq__ without __hash__ silently sets __hash__ = None on the
class — that left Number unusable as a set member, dict key, or
lru_cache argument. The new __hash__ uses the canonical fixed-point
string at the configured precision so it agrees with __eq__: two
Numbers that compare equal share that formatted form.
Regression test in tests/test_number_hashable.py exercises set
deduplication, dict-key lookup, and the a == b → hash(a) == hash(b)
contract for equivalent forms like Number("1") and Number("1.0").
See ai/improvements_2026-05-09.md item #6.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This was referenced May 11, 2026
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Problem. Python silently sets
__hash__ = Noneon any class that overrides__eq__without defining__hash__.Numberhad__eq__but no__hash__, so{Number("1"), Number("2")}raisedTypeError: unhashable type: 'Number'— andNumbercouldn't be a dict key or anlru_cacheargument either.Fix.
src/formula/formula.py— add__hash__that hashes the canonical fixed-point string at the configured precision. TwoNumberinstances that compare equal via__eq__share that canonical form, satisfying Python'sa == b ⇒ hash(a) == hash(b)contract.Test. New file
tests/test_number_hashable.pycovers set deduplication, dict-key lookup, and the hash/eq agreement for equivalent forms likeNumber("1")andNumber("1.0"). All pass; full suite 320/320.