Closed
Description
- cattrs version: 23.1.2
- Python version: 3.10.12
- Operating System: Linux (Ubuntu 22.04)
Description
I tried to mix cattrs.strategies.configure_tagged_union with a converter configured with forbid_extra_keys=True. Ideally this would work out of the box — structuring would remove the _type key before structuring the specific union member. Failing that this should be mentioned in the docs.
What I Did
Given tagged_union.py:
import attrs
from cattrs import Converter
from cattrs.strategies import configure_tagged_union
@attrs.define
class A:
pass
@attrs.define
class B:
pass
c = Converter(forbid_extra_keys=True)
configure_tagged_union(A | B, c)
data = c.unstructure(A(), A | B)
print(data)
c.structure(data, A | B)I get an exception because of the _type keys that the tagged union strategy injects:
❯ python tagged_union.py
{'_type': 'A'}
+ Exception Group Traceback (most recent call last):
| File ".../tagged_union.py", line 21, in <module>
| c.structure(data, A | B)
| File ".../venv/lib/python3.10/site-packages/cattrs/converters.py", line 334, in structure
| return self._structure_func.dispatch(cl)(obj, cl)
| File ".../venv/lib/python3.10/site-packages/cattrs/converters.py", line 651, in _structure_union
| return handler(obj, union)
| File ".../venv/lib/python3.10/site-packages/cattrs/strategies/_unions.py", line 86, in structure_tagged_union
| return _tag_to_cl[val[_tag_name]](val)
| File ".../venv/lib/python3.10/site-packages/cattrs/strategies/_unions.py", line 52, in structure_union_member
| return _h(val, _cl)
| File "<cattrs generated structure __main__.A>", line 7, in structure_A
| if errors: raise __c_cve('While structuring ' + 'A', errors, __cl)
| cattrs.errors.ClassValidationError: While structuring A (1 sub-exception)
+-+---------------- 1 ----------------
| cattrs.errors.ForbiddenExtraKeysError: Extra fields in constructor for A: _type
+------------------------------------