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Dataclass inheritance doesn't work when base class is decoded first #598
Description
Description
When using inheritance in dataclasses, msgspec decodes a derived class as it's base class when the base class is decoded once beforehand. I've made an minimal example to replicate the issue.
a.py:
from dataclasses import dataclass
@dataclass
class Base:
a: int
@dataclass
class Foo(Base):
b: intb.py:
import msgspec
def test_decode():
# Base class decoded first
from a import Base
x = Base(a=1)
ser = msgspec.json.encode(x)
dser = msgspec.json.decode(ser, type=Base)
assert x == dser
from a import Foo
x = Foo(a=1, b=2)
ser = msgspec.json.encode(x)
dser = msgspec.json.decode(ser, type=Foo)
assert x == dser
if __name__ == "__main__":
test_decode()Running pytest:
pytest b.py===================================================== test session starts =====================================================
platform linux -- Python 3.11.6, pytest-7.4.3, pluggy-1.3.0
rootdir: /tmp/
plugins: anyio-4.0.0
collected 2 items
b.py F [100%]
========================================================== FAILURES ===========================================================
_________________________________________________________ test_decode _________________________________________________________
def test_decode():
from a import Base
x = Base(a=1)
ser = msgspec.yaml.encode(x)
dser = msgspec.yaml.decode(ser, type=Base)
assert x == dser
from a import Foo
x = Foo(a=1, b=2)
ser = msgspec.yaml.encode(x)
dser = msgspec.yaml.decode(ser, type=Foo)
> assert x == dser
E assert Foo(a=1, b=2) == Base(a=1)
b.py:20: AssertionError
=================================================== short test summary info ===================================================
FAILED b.py::test_decode - assert Foo(a=1, b=2) == Base(a=1)
====================================================== 1 failed in 0.04s ======================================================
However, if the derived class is decoded first then the base class is correctly decoded. This works perfectly:
def test_decode():
# derived class decoded first
from a import Foo
x = Foo(a=1, b=2)
ser = msgspec.yaml.encode(x)
dser = msgspec.yaml.decode(ser, type=Foo)
assert x == dser
from a import Base
x = Base(a=1)
ser = msgspec.yaml.encode(x)
dser = msgspec.yaml.decode(ser, type=Base)
assert x == dserTested with:
- Python 3.11.6 and 3.9.18
- msgspec 0.18.4
Activity
jcrist commentedon Dec 4, 2023
Thanks for the excellent issue report - this was a subtle issue in our caching implementation. Fixed in #599.