`from pydantic import RootModel` fails in Python 3.10.0

[randomir]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

The problem

RootModel import on Python 3.10.0 (and only 3.10.0) fails with:

...
  File "<snipped>/lib/python3.10/site-packages/pydantic/root_model.py", line 26, in <module>
    class RootModel(BaseModel, typing.Generic[RootModelRootType]):
  File "<snipped>/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 172, in __new__
    set_model_fields(cls, bases, config_wrapper, types_namespace)
  File "<snipped>/lib/python3.10/site-packages/pydantic/_internal/_model_construction.py", line 400, in set_model_fields
    fields, class_vars = collect_model_fields(cls, bases, config_wrapper, types_namespace, typevars_map=typevars_map)
  File "<snipped>/lib/python3.10/site-packages/pydantic/_internal/_fields.py", line 98, in collect_model_fields
    type_hints = get_cls_type_hints_lenient(cls, types_namespace)
  File "<snipped>/lib/python3.10/site-packages/pydantic/_internal/_typing_extra.py", line 212, in get_cls_type_hints_lenient
    hints[name] = eval_type_lenient(value, globalns, localns)
  File "<snipped>/lib/python3.10/site-packages/pydantic/_internal/_typing_extra.py", line 221, in eval_type_lenient
    value = _make_forward_ref(value, is_argument=False, is_class=True)
TypeError: ForwardRef.__init__() got an unexpected keyword argument 'is_class'

The problem does not exist on 3.10.1+.

Seems like the reason is already described here, but for Python 3.9.

The fix

Since Pydantic depends on bpo-45166 fix to get_type_hints, and that fix was only included in 3.10.1 (was not present in 3.10.0), the hard-coded python version for 3.9 branch here:

pydantic/pydantic/_internal/_typing_extra.py

Line 256 in b33a795

if sys.version_info < (3, 9, 8):

should be expanded to include the bpo-45166 fix in the 3.10 branch as well.

Example Code

from pydantic import RootModel

Python, Pydantic & OS Version

pydantic version: 2.1.1
        pydantic-core version: 2.4.0
          pydantic-core build: profile=release pgo=true mimalloc=true
                 install path: /<omitted>/lib/python3.10/site-packages/pydantic
               python version: 3.10.0 (default, Nov 24 2021, 12:59:45) [GCC 5.4.0 20160609]
                     platform: Linux-4.15.0-142-generic-x86_64-with-glibc2.23
     optional deps. installed: ['typing-extensions']

Selected Assignee: @Kludex

[dmontagu]

It seems to me the fix might be changing the line to:

if sys.version_info < (3, 9, 8) or sys.version_info == (3, 10, 0): 

Is that what you meant?

If so, @randomir If you have a python 3.10.0 environment handy, would you mind testing and opening a PR for this?

(If that's wrong, PR still welcome to fix it.)

Thanks!

[randomir]

You're right @dmontagu, I opened #6919. Verified it in 3.10.0.