Initial Checks
Description
I encountered a crash in the mypy plugin. It happens in a particular situation when inheriting from a pydantic base class and overriding a member with a NewType. AFAIK the NewType has to be defined in another file and imported for it to crash.
You can find the minimal reproduction code here (as it needs multiple files): https://github.com/chaosct/pydantic_mypy_newtype_override
Then when running mypy:
uv run mypy consumer.py
Uninstalled 1 package in 76ms
Installed 1 package in 28ms
/Users/protopixel/Documents/projects/pydantic_mypy_newtype_override/reduced_case9/broken.py:5: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.19.1
Traceback (most recent call last):
File "mypy/semanal.py", line 7568, in accept
File "mypy/nodes.py", line 1478, in accept
File "mypy/semanal.py", line 1827, in visit_class_def
File "mypy/semanal.py", line 2044, in analyze_class
File "mypy/semanal.py", line 2091, in analyze_class_body_common
File "mypy/semanal.py", line 2176, in apply_class_plugin_hooks
File "/Users/protopixel/Documents/projects/pydantic_mypy_newtype_override/.venv/lib/python3.13/site-packages/pydantic/mypy.py", line 162, in _pydantic_model_class_maker_callback
transformer.transform()
~~~~~~~~~~~~~~~~~~~~~^^
File "/Users/protopixel/Documents/projects/pydantic_mypy_newtype_override/.venv/lib/python3.13/site-packages/pydantic/mypy.py", line 466, in transform
fields, class_vars = self.collect_fields_and_class_vars(config, is_a_root_model)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/protopixel/Documents/projects/pydantic_mypy_newtype_override/.venv/lib/python3.13/site-packages/pydantic/mypy.py", line 630, in collect_fields_and_class_vars
self._api.fail(
~~~~~~~~~~~~~~^
'BaseModel field may only be overridden by another field',
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
sym_node.node,
^^^^^^^^^^^^^^
)
^
File "mypy/semanal.py", line 7543, in fail
AttributeError: attribute 'column' of 'Context' undefined
/Users/protopixel/Documents/projects/pydantic_mypy_newtype_override/reduced_case9/broken.py:5: : note: use --pdb to drop into pdbInterestingly enough, if we use Field in the derived class, it won't crash:
# changed in reduced_case9/broken.py
class Broken(Base):
# attrs: AttrDict = AttrDict({"x": True}) # this was crashing
attrs: AttrDict = Field(default_factory=lambda: AttrDict({"x": True}))Then:
uv run mypy consumer.py
Success: no issues found in 1 source file
Example Code
Python, Pydantic & OS Version
pydantic version: 2.12.5
pydantic-core version: 2.41.5
pydantic-core build: profile=release pgo=false
python version: 3.13.7 (main, Sep 2 2025, 14:05:52) [Clang 20.1.4 ]
platform: macOS-14.5-arm64-arm-64bit-Mach-O
related packages: mypy-1.19.1 typing_extensions-4.15.0
commit: unknown
Initial Checks
Description
I encountered a crash in the mypy plugin. It happens in a particular situation when inheriting from a pydantic base class and overriding a member with a NewType. AFAIK the NewType has to be defined in another file and imported for it to crash.
You can find the minimal reproduction code here (as it needs multiple files): https://github.com/chaosct/pydantic_mypy_newtype_override
Then when running mypy:
Interestingly enough, if we use Field in the derived class, it won't crash:
Then:
Example Code
Python, Pydantic & OS Version