Unexpected error message while using properties with pydantic models

[bcdurak]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

Hello,

I ran into an issue while using a property with a pydantic class which led to an unexpected error.

To reproduce this error, you can simply create a pydantic class, define a property in it, and raise an AttributeError inside the property function. Instead of displaying this error, the stack trace will say:

AttributeError: 'MyModel' object has no attribute 'my_property'

Important to note, that this is the case only if extra is set to "allow" in the corresponding ConfigDict. If this line is disabled, the code raises the right error.

While it seems simple to see what the root cause of the failure is here in the example code, in complicated cases (where the call on the property executes some logic that ultimately leads to an AttributeError), this can be problematic and confusing as this does not showcase the correct error.

Example Code

from pydantic import BaseModel, ConfigDict


class MyModel(BaseModel):

    @property
    def my_property(self):
        """A random property."""
        raise AttributeError("Original Error!")

    model_config = ConfigDict(extra="allow")


my_model = MyModel()
my_model.my_property

Python, Pydantic & OS Version

pydantic version: 2.6.4
pydantic-core version: 2.16.3
pydantic-core build: profile=release pgo=false
install path: /Users/bariscandurak/.pyenv/versions/3.9.16/envs/zenml-temp/lib/python3.9/site-packages/pydantic
python version: 3.9.16 (main, Mar 11 2024, 18:29:02)  [Clang 14.0.3 (clang-1403.0.22.14.1)]
platform: macOS-13.5.1-arm64-arm-64bit
related packages: fastapi-0.110.0 typing_extensions-4.10.0 mypy-1.7.1 pydantic-settings-2.2.1
commit: unknown

[sydney-runkle]

@bcdurak,

Huh, that's odd! Thanks for reporting. Definitely a bug. Happens when you have the computed_field decorator over said property as well, which is even more concerning.

[NeevCohen]

@sydney-runkle I looked into this and it seems that the problem is in the Model.__getattr__() method.

try:
    pydantic_extra = object.__getattribute__(self, '__pydantic_extra__')
except AttributeError:
    pydantic_extra = None

if pydantic_extra is not None:
    try:
        return pydantic_extra[item]
    except KeyError as exc:
        raise AttributeError(f'{type(self).__name__!r} object has no attribute {item!r}') from exc
# ...
# Regular attribute handling continues here

When setting extra=True in model_config, __pydantic_extra__ is defined as an empty dictionary. That means that execution will enter this if block and try to get the attribute from the __pydantic_extra__ dict, which would be wrong.
I changed the if statement to be

if pydantic_extra:

That seems to fix the issue.

I opened a PR #9082

[bcdurak]

Thank you @NeevCohen @sydney-runkle!