I am currently testing a flow in my local machine. This flow was smoothly working before, but after some package updates, and etc, I encountered a very weird error while trying to execute any prefect flow. To diagnose what’s going on, I was checking slack threads, and one of the suggestion I figured out was to check the prefect version. And surprisingly, while printing prefect version, I got exactly the same error I observed while running my flow before. It seems like there is some issue with my current prefect package? Here is the error log:

(ENV_NAME) ➜  FOLDER_NAME git:(BRANCH_NAME) ✗ prefect version
Traceback (most recent call last):
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/cli/_utilities.py", line 41, in wrapper
    return fn(*args, **kwargs)
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/utilities/asyncutils.py", line 255, in coroutine_wrapper
    return call()
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/_internal/concurrency/calls.py", line 398, in __call__
    return self.result()
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/_internal/concurrency/calls.py", line 284, in result
    return self.future.result(timeout=timeout)
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/_internal/concurrency/calls.py", line 168, in result
    return self.__get_result()
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/concurrent/futures/_base.py", line 391, in __get_result
    raise self._exception
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/_internal/concurrency/calls.py", line 355, in _run_async
    result = await coro
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/cli/root.py", line 110, in version
    from prefect.server.utilities.database import get_dialect
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/server/__init__.py", line 1, in <module>
    from . import models, orchestration, schemas, services
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/server/models/__init__.py", line 1, in <module>
    from . import (
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/server/models/agents.py", line 13, in <module>
    from prefect.server.database.dependencies import inject_db
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/server/database/dependencies.py", line 14, in <module>
    from prefect.server.database.interface import PrefectDBInterface
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/server/database/interface.py", line 9, in <module>
    from prefect.server.database.query_components import BaseQueryComponents
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/server/database/query_components.py", line 26, in <module>
    from prefect.server.schemas.graph import Edge, Graph, Node
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/site-packages/prefect/server/schemas/graph.py", line 13, in <module>
    class Node(PrefectBaseModel):
  File "pydantic/main.py", line 197, in pydantic.main.ModelMetaclass.__new__
  File "pydantic/fields.py", line 506, in pydantic.fields.ModelField.infer
  File "pydantic/fields.py", line 436, in pydantic.fields.ModelField.__init__
  File "pydantic/fields.py", line 552, in pydantic.fields.ModelField.prepare
  File "pydantic/fields.py", line 668, in pydantic.fields.ModelField._type_analysis
  File "/Users/MYNAME/miniforge3/envs/ENV_NAME/lib/python3.9/typing.py", line 852, in __subclasscheck__
    return issubclass(cls, self.__origin__)
TypeError: issubclass() arg 1 must be a class
An exception occurred.

Indeed,

TypeError: issubclass() arg 1 must be a class

is what is constantly irritating me.

this appears to be a compatibility issue between

pydantic

and `typing`: https://github.com/pydantic/pydantic/issues/5821 It looks like the solutions suggested in that thread are any one of: • upgrade to python 3.10 • upgrade pydantic • upgrade

typing_extensions

Thanks. I fixed this by downgrading prefect to version 2.10.17. Though, I will check your answers too, so I can keep my prefect library version as up-to-date as possible!