Sample

Author custom validators, converters, default factories, and custom serializers in attrs without falling into decorator illusions, signature mismatches, or serialization key drift

sha256:04534868bcf83a1c9437d56575f5b38eea5b61ac3a126103d53fa34f2fbd7310

Case

Goal

Author custom validators, converters, default factories, and custom serializers in attrs without falling into decorator illusions, signature mismatches, or serialization key drift HOW

Packages

attrs 26.1.0

Environment

python 3.12

Created

2026-08-17T03:18:45Z

Contract

• assert custom @field.validator methods require (self, attribute, value) and fail with TypeError when defined with (self, value)
• assert validator return values are discarded and do not mutate the attribute value
• assert @username.validator on top of field(validator=[...]) chains all checks in sequence via _AndValidator
• assert validators.matches_re uses anchored re.match by default and rejects non-prefix matches
• assert validators.in_(Enum) follows Python 3.12 Enum membership: raw member values are accepted without conversion while absent values raise ValueError
• assert validators.not_ raises ValueError when the inner validator does not raise
• assert validators.deep_iterable and deep_mapping validate container types and all child items or key-value pairs
• assert validator=[optional(instance_of(int)), gt(0)] fails on None with TypeError because gt(0) still runs on None, while optional(and_(...)) protects the composite
• assert @field.converter does not exist on _CountingAttr and raises TypeError at class definition because field().converter is None
• assert converter=int with default=None crashes on __init__ with TypeError because converters execute on default values, requiring converters.optional(int)
• assert converters.pipe with default_if_none and to_bool chains fallback replacement and boolean conversion
• assert attrs.Converter(takes_self=True, takes_field=True) allows converters to receive (value, self, field) while raw 2-arg callables fail with TypeError
• assert on_setattr custom setters execute only on attribute assignment and never during __init__
• assert attrs permits default=[] without error at class definition, silently creating shared mutable state across instances
• assert Factory(takes_self=True) and @field.default compute dynamic defaults from self during initialization
• assert passing both default= and factory= to attrs.field raises ValueError
• assert attrs.asdict keys by attribute.name and not attribute.alias, causing Class(**attrs.asdict(obj)) to fail with TypeError on aliased fields
• assert attrs.asdict filter takes (attribute, value) -> bool and filters.exclude removes matching attributes
• assert attrs.asdict value_serializer requires (inst, field, value) and fails with TypeError on 2-arg callables
• assert attrs.evolve keys by alias and re-runs validators on new instances
• assert attrs.cmp_using customizes equality and ordering when order=True is set on class and field has both eq and order defined
• assert mandatory fields defined in a subclass after parent default fields raise ValueError at definition unless kw_only=True is specified

Files

• NOTES.md
• csx.json
• requirements.txt
• src/__init__.py
• src/models.py
• test/contract.py

Download the verified artifact (tar.gz) — the exact bytes the contract ran against

Origin Seeder

csx-seed

Verification receipts

• python 3.12 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · python@1 · 2026-08-17 · ed25519:d91480838ac982c9