Pydantic: TypeError: issubclass() arg 1 must be a class

Created on 25 May 2019 · 19Comments · Source: samuelcolvin/pydantic

Bug

Hi. I'm getting a type error when trying to generate a schema, using fastapi:

Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/uvicorn/protocols/http/httptools_impl.py", line 368, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "/usr/local/lib/python3.7/site-packages/starlette/applications.py", line 133, in __call__
    await self.error_middleware(scope, receive, send)
  File "/usr/local/lib/python3.7/site-packages/starlette/middleware/errors.py", line 122, in __call__
    raise exc from None
  File "/usr/local/lib/python3.7/site-packages/starlette/middleware/errors.py", line 100, in __call__
    await self.app(scope, receive, _send)
  File "/usr/local/lib/python3.7/site-packages/starlette/middleware/cors.py", line 76, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.7/site-packages/starlette/exceptions.py", line 73, in __call__
    raise exc from None
  File "/usr/local/lib/python3.7/site-packages/starlette/exceptions.py", line 62, in __call__
    await self.app(scope, receive, sender)
  File "/usr/local/lib/python3.7/site-packages/starlette/routing.py", line 585, in __call__
    await route(scope, receive, send)
  File "/usr/local/lib/python3.7/site-packages/starlette/routing.py", line 207, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.7/site-packages/starlette/routing.py", line 40, in app
    response = await func(request)
  File "/usr/local/lib/python3.7/site-packages/fastapi/applications.py", line 90, in openapi
    return JSONResponse(self.openapi())
  File "/usr/local/lib/python3.7/site-packages/fastapi/applications.py", line 82, in openapi
    openapi_prefix=self.openapi_prefix,
  File "/usr/local/lib/python3.7/site-packages/fastapi/openapi/utils.py", line 248, in get_openapi
    flat_models=flat_models, model_name_map=model_name_map
  File "/usr/local/lib/python3.7/site-packages/fastapi/utils.py", line 42, in get_model_definitions
    model, model_name_map=model_name_map, ref_prefix=REF_PREFIX
  File "/usr/local/lib/python3.7/site-packages/pydantic/schema.py", line 511, in model_process_schema
    model, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
  File "/usr/local/lib/python3.7/site-packages/pydantic/schema.py", line 537, in model_type_schema
    f, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
  File "/usr/local/lib/python3.7/site-packages/pydantic/schema.py", line 274, in field_schema
    ref_prefix=ref_prefix,
  File "/usr/local/lib/python3.7/site-packages/pydantic/schema.py", line 486, in field_type_schema
    ref_prefix=ref_prefix,
  File "/usr/local/lib/python3.7/site-packages/pydantic/schema.py", line 687, in field_singleton_schema
    if issubclass(field.type_, Enum):
TypeError: issubclass() arg 1 must be a class

For bugs/questions:

OS: uname -a Linux char-lang-dev 4.18.0-20-generic #21~18.04.1-Ubuntu SMP Wed May 8 08:43:37 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Python version import sys; print(sys.version): '3.7.1 (default, Oct 22 2018, 11:21:55) \n[GCC 8.2.0]'
Pydantic version import pydantic; print(pydantic.VERSION): '3.7.1 (default, Oct 22 2018, 11:21:55) \n[GCC 8.2.0]'

Where possible please include a self contained code snippet describing your
bug, question, or where applicable feature request:

from __future__ import annotations
from typing import Optional, List

from pydantic import BaseModel, UUID4


class CategoryCreationValidator(BaseModel):
    name: str = ...
    labels: List[str] = None
    description: str = ...
    parent_id: int = None


class CategorySelectionValidator(BaseModel):
    name: str = ...
    organization_id: str = ...
    labels: Optional[str] = None
    description: str = ...
    parent_id: Optional[int] = None


class CategoryUpdateValidator(BaseModel):
    name: Optional[str] = None
    organization_id: Optional[str] = None
    labels: Optional[List[str]] = None
    description: Optional[str] = None
    parent_id: Optional[int] = None


class ClusterValidator(BaseModel):
    name: str = ...
    category_id: Optional[str] = None


class CategoryModel(BaseModel):
    id: int = ...
    name: str = ...
    description: str = ...
    parent_id: int = None
    children: List[CategoryModel]


#CategoryModel.update_forward_refs()


class ClusterModel(BaseModel):
    id: UUID4 = ...
    name: str = ...
    parent_category_id: str = ...
    queries: List[str] = ...
    urls: List[str] = ...


class SuggestionValidator(BaseModel):
    queries: List[str] = ...
    urls: List[str] = ...


class QueryCreationValidator(BaseModel):
    query_text: str = ...
    cluster_id: UUID4 = ...


class QuerySelectionValidator(BaseModel):
    cluster_id: UUID4 = ...


class UrlCreationValidator(BaseModel):
    url: str = ...
    cluster_id: UUID4 = ...


class UrlSelectionValidator(BaseModel):
    cluster_id: UUID4 = ...


class CreateClusterInput(BaseModel):
    name: str = ...
    category_id: int = ...


class ClusterSelectionValidator(BaseModel):
    category_name: str = ...

...

bug help wanted

Source

DrPyser

Most helpful comment

pydantic==1.4
fastapi==0.52.0
python 3.7.4

issue persist

Casyfill on 6 Mar 2020

👍2

All 19 comments

Thanks for reporting.

@tiangolo, maybe this is as simple as using lenient_issubclass instead of issubclass?

samuelcolvin on 25 May 2019

Coincidentally, I just came here to report an issue about the same error. In my case, it happens when you create a subclass of BaseModel which specifies a field of type Dict which does not specify mapping types, i.e.:

from pydantic import BaseModel
from typing import Dict, Any

class SubclassThatWorks(BaseModel):
    asdf: int
    fdsa: Dict[Any, Any]

class SubclassThatFails(BaseModel):
    asdf: int
    fdsa: Dict

with the error message being:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/validators.py in find_validators(type_, arbitrary_types_allowed)
    385         try:
--> 386             if issubclass(type_, val_type):
    387                 return validators

TypeError: issubclass() arg 1 must be a class

The above exception was the direct cause of the following exception:

RuntimeError                              Traceback (most recent call last)
<ipython-input-5-c7b931439a60> in <module>
----> 1 class Subclass(BaseModel):
      2     asdf: int
      3     fdsa: Dict

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/main.py in __new__(mcs, name, bases, namespace)
    180                     annotation=ann_type,
    181                     class_validators=vg.get_validators(ann_name),
--> 182                     config=config,
    183                 )
    184 

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in infer(cls, name, value, annotation, class_validators, config)
    136             required=required,
    137             model_config=config,
--> 138             schema=schema,
    139         )
    140 

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in __init__(self, name, type_, class_validators, model_config, default, required, alias, schema)
    105         self.parse_json: bool = False
    106         self.shape: Shape = Shape.SINGLETON
--> 107         self.prepare()
    108 
    109     @classmethod

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in prepare(self)
    170             self.allow_none = True
    171 
--> 172         self._populate_sub_fields()
    173         self._populate_validators()
    174 

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in _populate_sub_fields(self)
    221             assert issubclass(origin, Mapping)
    222             self.key_field = self._create_sub_type(
--> 223                 self.type_.__args__[0], 'key_' + self.name, for_keys=True  # type: ignore
    224             )
    225             self.type_ = self.type_.__args__[1]  # type: ignore

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in _create_sub_type(self, type_, name, for_keys)
    235             name=name,
    236             class_validators=None if for_keys else {k: v for k, v in self.class_validators.items() if not v.whole},
--> 237             model_config=self.model_config,
    238         )
    239 

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in __init__(self, name, type_, class_validators, model_config, default, required, alias, schema)
    105         self.parse_json: bool = False
    106         self.shape: Shape = Shape.SINGLETON
--> 107         self.prepare()
    108 
    109     @classmethod

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in prepare(self)
    171 
    172         self._populate_sub_fields()
--> 173         self._populate_validators()
    174 
    175     def _populate_sub_fields(self) -> None:  # noqa: C901 (ignore complexity)

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/fields.py in _populate_validators(self)
    253                     get_validators()
    254                     if get_validators
--> 255                     else find_validators(self.type_, self.model_config.arbitrary_types_allowed)
    256                 ),
    257                 self.schema is not None and self.schema.const and constant_validator,

/scratch/miniconda3/envs/jupyter/lib/python3.7/site-packages/pydantic/validators.py in find_validators(type_, arbitrary_types_allowed)
    387                 return validators
    388         except TypeError as e:
--> 389             raise RuntimeError(f'error checking inheritance of {type_!r} (type: {display_as_type(type_)})') from e
    390 
    391     if arbitrary_types_allowed:

RuntimeError: error checking inheritance of ~KT (type: KT)

Not sure if this is because of a design decision that Dict types should have the mapping types explicitly defined or not, but the error message wasn't very clear as to what the problem was.

zbarry on 25 May 2019

sounds like a different problem, could you create a new issue and perhaps even a fix?

In the meantime you should be able to use just dict instead of Dict which will have the same effect but shouldn't fail.

samuelcolvin on 25 May 2019

👍1

@samuelcolvin Do you know a workaround for my situation? The doc uses List and Optional in its examples, so I'm confused on what is causing this?

DrPyser on 27 May 2019

Ok, I can confirm the issue is the self-reference(children: List[CategoryModel]). Using just list or List[Any] avoids the error.

DrPyser on 27 May 2019

👍1

Thanks for tagging me @samuelcolvin .

I think this is then a duplicate of https://github.com/samuelcolvin/pydantic/issues/531

I still have to check/fix the JSON Schema generation when using forward refs.

For @zbarry problem, you can use dict or Dict[Any, Any]. But that's has a separate issue now.

tiangolo on 27 May 2019

👍1

Hit this one, I think, with very simple reproduction:

from typing import NewType

from pydantic import BaseModel

Age = NewType("Age", int)

class Person(BaseModel):
    age: Age

Similar issue when generating schema in FastAPI.

So far using class Age(int): pass as a workaround.

haizaar on 2 Jun 2019

👍1

Removing from __future__ import annotations fixed this issue for me. However, it would be cool if there would be support for this.

georgw777 on 4 Jun 2019

I don't have from __future__ import annotations in my code btw.

haizaar on 17 Jun 2019

@haizaar This is fixed in the current version of pydantic (v0.28), with or without the __future__ import. Or at least, I am able to run the code snippet you provided above (in python 3.7.3) without any errors.

dmontagu on 17 Jun 2019

🎉2

@DrPyser I'm not sure what was the problem, maybe it was fixed recently in Pydantic or in FastAPI.

But here's a slightly modified (without from __future__ import annotations) self-contained working app:

from typing import List, Optional

from pydantic import UUID4, BaseModel

from fastapi import FastAPI


class CategoryCreationValidator(BaseModel):
    name: str = ...
    labels: List[str] = None
    description: str = ...
    parent_id: int = None


class CategorySelectionValidator(BaseModel):
    name: str = ...
    organization_id: str = ...
    labels: Optional[str] = None
    description: str = ...
    parent_id: Optional[int] = None


class CategoryUpdateValidator(BaseModel):
    name: Optional[str] = None
    organization_id: Optional[str] = None
    labels: Optional[List[str]] = None
    description: Optional[str] = None
    parent_id: Optional[int] = None


class ClusterValidator(BaseModel):
    name: str = ...
    category_id: Optional[str] = None


class CategoryModel(BaseModel):
    id: int = ...
    name: str = ...
    description: str = ...
    parent_id: int = None
    children: List["CategoryModel"]


CategoryModel.update_forward_refs()


class ClusterModel(BaseModel):
    id: UUID4 = ...
    name: str = ...
    parent_category_id: str = ...
    queries: List[str] = ...
    urls: List[str] = ...


class SuggestionValidator(BaseModel):
    queries: List[str] = ...
    urls: List[str] = ...


class QueryCreationValidator(BaseModel):
    query_text: str = ...
    cluster_id: UUID4 = ...


class QuerySelectionValidator(BaseModel):
    cluster_id: UUID4 = ...


class UrlCreationValidator(BaseModel):
    url: str = ...
    cluster_id: UUID4 = ...


class UrlSelectionValidator(BaseModel):
    cluster_id: UUID4 = ...


class CreateClusterInput(BaseModel):
    name: str = ...
    category_id: int = ...


class ClusterSelectionValidator(BaseModel):
    category_name: str = ...



app = FastAPI()


@app.post("/")
def main(
    a: CategoryCreationValidator,
    b: CategorySelectionValidator,
    c: CategoryUpdateValidator,
    d: ClusterValidator,
    e: CategoryModel,
    f: ClusterModel,
    g: SuggestionValidator,
    h: QueryCreationValidator,
    i: QuerySelectionValidator,
    j: UrlCreationValidator,
    k: UrlSelectionValidator,
    l: CreateClusterInput,
    m: ClusterSelectionValidator,
):
    return {"message": "Hello World"}

tiangolo on 20 Jun 2019

👍1

@tiangolo Yup, I think I've tested that everything now works after updating. Thanks everyone!

DrPyser on 22 Jun 2019

Great! I'll close this issue now then.

tiangolo on 28 Jun 2019

👍1

Having the same issue:

class ModelName(str, Enum):
    repeated_sale = "repeated_sale"
    main = "main"
    dummy = "dummy"


class Inference(BaseModel):
    price: int
    model: ModelName
    model_version: float
    date: date

@app.get("/infer", response_model=Inference)
def infer(
    params: dict,
    model: ModelName,
    v: Optional[float] = None,
    date: Optional["date"] = None,
) -> Inference:
    """attempts to pull predictions from snowflake"""
    result = app.model_registry.pull(model=model, v=v, date=date).predict(params)
    return {"model": model, "v": v, **result}

results in:

  File "/Users/philippk/anaconda3/envs/py37/lib/python3.7/site-packages/pydantic/schema.py", line 657, in field_singleton_schema
    if issubclass(field_type, Enum):
TypeError: issubclass() arg 1 must be a class

python 3.7
pydantic==1.4.0
fastapi==0.49.0

Casyfill on 26 Feb 2020

@Casyfill I can't reproduce that error with fastapi 0.52.0 and python 3.8.

Can you try updating your fastapi version and seeing if you still have issues? If so, could you share a full self-contained example (including import statements etc.)?

Also, I'd recommend creating a new issue if there is still a bug as it likely differs enough from this issue to be worth tracking separately (and having the issue be open makes it easier to prioritize).

dmontagu on 4 Mar 2020

pydantic==1.4
fastapi==0.52.0
python 3.7.4

issue persist

Casyfill on 6 Mar 2020

👍2

Could you put together a self-contained reproducible example? If you can do that I'm happy to debug/submit a PR to fix it.

dmontagu on 7 Mar 2020

Could you put together a self-contained reproducible example? If you can do that I'm happy to debug/submit a PR to fix it.

Here: https://github.com/samuelcolvin/pydantic/issues/1298#issuecomment-607842409

half2me on 2 Apr 2020

Submit same trouble as @half2me

m3xan1k on 5 Apr 2020

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