mypy INTERNAL ERROR: maximum semantic analysis iteration count reached

[brianmedigate]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

The code below causes mypy to crash with INTERNAL ERROR: maximum semantic analysis iteration count reached.
It reproduces on pydantic 2.6.0 with the pydantic.mypy plugin enabled.
It does not reproduce on pydantic 2.5.3 or without the plugin.

The minimal reproducible example below is a bit strange and arbitrary. I have distilled it from a real codebase. It is not clear at all how the parts come together to cause the behavior, but almost any significant change to the code will solve the problem:

• if the pydantic field isn't Optional
• if the pydantic model isn't subclassed
• if the NamedTuple doesn't have a method

Example Code

from typing import NamedTuple, Optional

from pydantic import BaseModel


class A(BaseModel):
    a: Optional[str]


class B(A):
    pass


class What(NamedTuple):
    foo: str

    def bar(self) -> None:
        pass

Python, Pydantic & OS Version

pydantic version: 2.6.0
        pydantic-core version: 2.16.1
          pydantic-core build: profile=release pgo=true
                 install path: /home/brianm/repos/medigator/venv/lib/python3.8/site-packages/pydantic
               python version: 3.8.18 (default, Aug 25 2023, 13:20:30)  [GCC 11.4.0]
                     platform: Linux-6.1.0-1029-oem-x86_64-with-glibc2.35
             related packages: email-validator-2.1.0.post1 typing_extensions-4.9.0 fastapi-0.109.0 pydantic-settings-2.1.0 mypy-1.8.0
                       commit: unknown

[sydney-runkle]

I believe this is a duplicate of #8665 which was resolved with #8666. That fix is now live with 2.6.1.

[sydney-runkle]

@brianmedigate,

Could you please check if you're still having this issue with 2.6.1? Thanks!

[brianmedigate]

Replicates in 2.6.1, unfortunately

$ python -c "import pydantic.version; print(pydantic.version.version_info())"
             pydantic version: 2.6.1
        pydantic-core version: 2.16.2
          pydantic-core build: profile=release pgo=true
                 install path: .../venv/lib/python3.8/site-packages/pydantic
               python version: 3.8.18 (default, Aug 25 2023, 13:20:30)  [GCC 11.4.0]
                     platform: Linux-6.1.0-1029-oem-x86_64-with-glibc2.35
             related packages: email-validator-2.1.0.post1 typing_extensions-4.9.0 fastapi-0.109.0 pydantic-settings-2.1.0 mypy-1.8.0
                       commit: unknown

[alexgaspard]

I have this issue as well with this sample:

from typing import Annotated, Optional, Union

from pydantic import BaseModel, Field, field_validator, model_validator


class Origin(BaseModel):
    x: Union[str, None]


def hello() -> None:
    class Test(Origin):

        @field_validator("x")
        @classmethod
        def validate_x(cls, value: Union[str, None]) -> Union[str, None]:
            if value is not None and value == "":
                raise ValueError("Not allowed")
            return value

mypy returns error: INTERNAL ERROR: maximum semantic analysis iteration count reached

I'm using python3.9 and have these versions installed:

mypy                         1.8.0
mypy-extensions              1.0.0
pydantic                     2.6.1
pydantic_core                2.16.2
pydantic-settings            2.1.0

[Cielquan]

I have this issue as well with the same mypy error. The issue starts to occur with version 2.6.0b1.

Minimal repro

This repro is a stripped down version of a config file from a real application. The config file uses pydantic_settings but the issue also occurs if I replace BaseSettings with BaseModel, so I guess it's an issue with pydantic.

"""Config for Application."""
from __future__ import annotations

import typing as t

# from pydantic_settings import BaseSettings
from pydantic import BaseModel as BaseSettings


class CustomBaseSettings(BaseSettings):
    """Custom base settings class with added functionality and set base config."""


class MySQLSettings(CustomBaseSettings):
    """MySQL settings with partial defaults."""

    DB_MYSQL_PASSWORD: str | None


class Settings(t.Protocol):
    """Application Settings protocol."""

    DB_MYSQL_SETTINGS: MySQLSettings | None


class _SettingsBase(CustomBaseSettings):
    """Shareable base settings."""

    DB_MYSQL_SETTINGS: MySQLSettings | None = None


def get_prod_settings() -> Settings:
    """Return cached Production settings."""

    class ProdMySQLSettings(MySQLSettings):
        """Production MySQL settings."""

    class ProdSettings(_SettingsBase):
        """Production application settings."""

        DB_MYSQL_SETTINGS: MySQLSettings | None = ProdMySQLSettings()

    return ProdSettings()

Versions

Python:

$ python3 -VV
Python 3.11.7 (main, Dec  8 2023, 18:56:58) [GCC 11.4.0]

Dependencies:

pydantic==2.6.4
pydantic-settings==2.2.1
pydantic_core==2.16.3
mypy==1.9.0
mypy-extensions==1.0.0

Mypy Config

Mypy config in pyproject.toml:

[tool.mypy]
python_version = "3.11"
mypy_path = "mypy_stubs"
follow_imports = "silent"
disallow_any_generics = true
disallow_subclassing_any = true
disallow_untyped_defs = true
check_untyped_defs = true
strict_optional = true
warn_redundant_casts = true
warn_unused_ignores = true
warn_return_any = true
warn_unreachable = true
implicit_reexport = false
show_error_context = true
show_column_numbers = true
plugins = ["pydantic.mypy"]

[tool.pydantic-mypy]
init_forbid_extra = true
init_typed = false
warn_required_dynamic_aliases = true

[dmontagu]

I believe this is all fixed by #9008, which should be included in the next release.

[Cielquan]

I just tested against main at commit a3b7214 and can confirm the issue is gone for my example.