Error While Structuring Final Sequences

[dtoniolo]

Versions

• cattrs version: 23.1.2
• Python version: 3.11
• Operating System: Ubuntu 22.03

Description

Hi, first of all I want to thank you for adding the support for structuring and destructuring of Final attributes in cattrs 23. I've been using it throughout my codebase ever since and it's proven very useful. Unfortunately, I might have run into a bug of this new feature. In particular, cattrs fails when attempting to structure Final sequences.

Example

The following minimal example

from typing import Final
import attr
from cattrs.preconf.json import JsonConverter

@attr.s(init=True)
class Foo:
    foo: Final[list[float]] = attr.ib()

converter = JsonConverter()
converter.loads('{ "foo": [0.12] }', Foo)

results in the error

---------------------------------------------------------------------------
ClassValidationError                      Traceback (most recent call last)
Cell In[2], line 11
      8     foo: Final[list[float]] = attr.ib()
     10 converter = JsonConverter()
---> 11 converter.loads('{ "foo": [0.12] }', Foo)

File ... python3.11/site-packages/cattrs/preconf/json.py:19, in JsonConverter.loads(self, data, cl, **kwargs)
     18 def loads(self, data: Union[bytes, str], cl: Type[T], **kwargs: Any) -> T:
---> 19     return self.structure(loads(data, **kwargs), cl)

File ... python3.11/site-packages/cattrs/converters.py:334, in BaseConverter.structure(self, obj, cl)
    332 def structure(self, obj: Any, cl: Type[T]) -> T:
    333     """Convert unstructured Python data structures to structured data."""
--> 334     return self._structure_func.dispatch(cl)(obj, cl)

File <cattrs generated structure __main__.Foo>:9, in structure_Foo(o, _, __cl, __c_cve, __c_avn, __c_structure_foo, __c_type_foo)
      7   e.__notes__ = getattr(e, '__notes__', []) + [__c_avn("Structuring class Foo @ attribute foo", "foo", __c_type_foo)]
      8   errors.append(e)
----> 9 if errors: raise __c_cve('While structuring ' + 'Foo', errors, __cl)
     10 try:
     11   return __cl(

ClassValidationError: While structuring Foo (1 sub-exception)

The same issue happens also if a tuple or a generic Sequence are used instead of a list. Moreover, if the Final from the definition of Foo is removed, then the json string is structured correctly and without errors.

[Tinche]

You're right, can confirm. I'll put this into the next release milestone so it gets looked at before the release. Thanks!

[dtoniolo]

Awesome, thank you!