Self-referencing model in python 3.6 fails #616
Description
Question/Bug
- OS: Debian Stretch
- Python version: 3.6.5
- Pydantic version : 0.29
I am not sure, self-referencing models are supported under python 3.6.x. The doc seems to describe it, but testing it it failed for me:
Using self-contained script from doc saved as self_ref.py:
from pydantic import BaseModel
class Foo(BaseModel):
a: int = 123
#: The sibling of `Foo` is referenced by string
sibling: 'Foo' = None
Foo.update_forward_refs()
print(Foo())
#> Foo a=123 sibling=None
print(Foo(sibling={'a': '321'}))
#> Foo a=123 sibling=<Foo a=321 sibling=None>Run under python 3.7.3 (OK)
(py37) $ python self_ref.py
Foo a=123 sibling=None
Foo a=123 sibling=<Foo a=321 sibling=None>Run under python 3.6.5 (failure)
(py36) $ python self_ref.py
Traceback (most recent call last):
File "pydantic/validators.py", line 431, in pydantic.validators.find_validators
TypeError: issubclass() arg 1 must be a class
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "self_ref.py", line 3, in <module>
class Foo(BaseModel):
File "pydantic/main.py", line 206, in pydantic.main.MetaModel.__new__
File "pydantic/fields.py", line 130, in pydantic.fields.Field.infer
File "pydantic/fields.py", line 107, in pydantic.fields.Field.__init__
File "pydantic/fields.py", line 173, in pydantic.fields.Field.prepare
File "pydantic/fields.py", line 262, in pydantic.fields.Field._populate_validators
File "pydantic/validators.py", line 440, in find_validators
RuntimeError: error checking inheritance of 'Foo' (type: str)