The underscore_attrs_are_private config flag turns __doc__ attribute into a ModelPrivateAttr

[jstavrak]

Checks

• I added a descriptive title to this issue
• I have searched (google, github) for similar issues and couldn't find anything
• I have read and followed the docs and still think this is a bug

Bug

Output of python -c "import pydantic.utils; print(pydantic.utils.version_info())":

             pydantic version: 1.7.2
            pydantic compiled: False
                 install path: D:\dev\Miniconda3\envs\geoenv\Lib\site-packages\pydantic
               python version: 3.8.6 | packaged by conda-forge | (default, Oct  7 2020, 18:22:52) [MSC v.1916 64 bit (AMD64)]
                     platform: Windows-10-10.0.19041-SP0
     optional deps. installed: ['typing-extensions']

Pydantic v1.7 introduced the private attributes. But when the config flag underscore_attrs_are_private is set to True, the model's __doc__ attribute also becomes a private attribute. Example:

>>> from pydantic import BaseModel
>>> class MyModel(BaseModel):
...     """MyModel docsting."""
...     class Config:
...         underscore_attrs_are_private = True
...
>>> MyModel.__doc__
<member '__doc__' of 'MyModel' objects>

My current workaround is to define a new metaclass to handle the issue:

>>> from pydantic import BaseModel
>>> from pydantic.main import ModelMetaclass
>>> from pydantic.fields import ModelPrivateAttr
>>> class DocPreservingModelMetaclass(ModelMetaclass):
...     def __new__(mcs, name, bases, namespace, **kwargs):
...         cls = super().__new__(mcs, name, bases, namespace, **kwargs)
...         if cls.__config__.underscore_attrs_are_private:
...             doc = cls.__private_attributes__.pop('__doc__', None)
...             if isinstance(doc, ModelPrivateAttr):
...                 cls.__doc__ = doc.default
...         return cls
...
>>> class MyModel(BaseModel, metaclass=DocPreservingModelMetaclass):
...     """MyModel docsting."""
...     class Config:
...         underscore_attrs_are_private = True
...
>>> MyModel.__doc__
'MyModel docsting.'

But maybe it would be best if __doc__ was excluded via pydantic.utils.is_valid_private_name, much like the other standard properties are excluded through this method. However, I am not sure if the latter will have other implication in the current codebase.

[PrettyWood]

Hi @jstavrak
Thanks for reporting! You're absolutely right I just made a quick fix. In the meantime your workaround seems good though the new metaclass could be simplified a bit

class DocPreservingModelMetaclass(ModelMetaclass):
     def __new__(mcs, name, bases, namespace, **kwargs):
         doc = namespace.pop('__doc__', None)
         cls = super().__new__(mcs, name, bases, namespace, **kwargs)
         cls.__doc__ = doc
         return cls

Have a good day

[jstavrak]

Hi guys,

Thanks for the immediate reply, fix, and simplification of the metaclass offered!

Have a nice day!