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Attribute on class itself

pyrefly/test_laziness/test_attribute_on_class_itself.md

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Attribute on class itself

Accessing c.child_attr where child_attr is defined on Child, not inherited from Base.

a -> b::KeyExport("Child") is necessary.

The demand tree is nearly identical to test_attribute_inherited — all the same class metadata, MRO, abstract check, and synthesized fields demands appear. This is because the attribute lookup code in attr.rs walks the FULL MRO for every attribute access, even when the attribute is found on the first class checked.

Superfluous demands:

  • ALL demands involving c (Base's module) are superfluous — child_attr is on Child, so Base is never needed.
  • a -> b::KeyAbstractClassCheck(0) is superfluous for attribute access (only needed for instantiation).
  • a -> b::KeyClassMro(0) and the cascading b -> c::* demands are superfluous — the MRO iterator trick would avoid materializing the MRO when the attribute is found on the class itself.

Files

a.py:

python
from b import Child
c = Child()
x = c.child_attr

b.py:

python
from c import Base
class Child(Base):
    child_attr: str = 'hello'

c.py:

python
class Base:
    base_attr: int = 1

Check a.py

expected
a: Solutions
b: Answers
c: Answers

(72 builtin demands hidden)
a -> b::Exports(is_special_export)
a -> b::Load(module_exists)
a -> b::Exports(export_exists)
a -> b::Exports(is_implicit_reexport)
a -> b::Exports(get_deprecated)
a -> b::KeyExport(Name("Child"))
  b -> c::Exports(is_special_export)
a -> b::KeyClassMetadata(ClassDefIndex(0))
  b -> c::Exports(export_exists)
  b -> c::Exports(is_implicit_reexport)
  b -> c::Exports(get_deprecated)
  b -> c::KeyExport(Name("Base"))
  b -> c::KeyClassMetadata(ClassDefIndex(0))
  b -> c::KeyClassMetadata(ClassDefIndex(0))
  b -> c::KeyClassMetadata(ClassDefIndex(0))
a -> b::KeyClassMetadata(ClassDefIndex(0))
a -> b::KeyAbstractClassCheck(ClassDefIndex(0))
  b -> c::KeyClassMetadata(ClassDefIndex(0))
a -> b::KeyClassSynthesizedFields(ClassDefIndex(0))
a -> b::KeyClassMro(ClassDefIndex(0))
  b -> c::KeyClassMetadata(ClassDefIndex(0))
  b -> c::KeyClassMetadata(ClassDefIndex(0))
  b -> c::KeyClassBaseType(ClassDefIndex(0))
  b -> c::KeyClassMro(ClassDefIndex(0))
a -> c::KeyClassSynthesizedFields(ClassDefIndex(0))
a -> b::KeyClassMro(ClassDefIndex(0))
a -> b::KeyClassField(ClassDefIndex(0), Name("child_attr"))