Can't put Callable in SQLModel even when not persisted

[alexkreidler]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the SQLModel documentation, with the integrated search.
• I already searched in Google "How to X in SQLModel" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to SQLModel but to Pydantic.
• I already checked if it is not related to SQLModel but to SQLAlchemy.

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Example Code

from typing import Callable, Optional
from sqlmodel import Field, SQLModel

print("start")

class BaseTool(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    description: str
    icon: Optional[str]
    # JSON schema of arguments
    args: str

print("middle")

class Tool(BaseTool):
    """Tool for use in-memory, includes the tool function. Should not be persisted directly to the DB"""
    func: Callable

print("end")

Description

1. run python test.py or python -m test
2. You should get this output

start
middle
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/root/c2/toddleragi/backend/agi/types/tool.py", line 16, in <module>
    class Tool(BaseTool):
  File "/root/micromamba/envs/agi/lib/python3.11/site-packages/sqlmodel/main.py", line 293, in __new__
    col = get_column_from_field(v)
          ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/micromamba/envs/agi/lib/python3.11/site-packages/sqlmodel/main.py", line 421, in get_column_from_field
    sa_type = get_sqlachemy_type(field)
              ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/micromamba/envs/agi/lib/python3.11/site-packages/sqlmodel/main.py", line 375, in get_sqlachemy_type
    if issubclass(field.type_, str):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: issubclass() arg 1 must be a class

The problem is that the Callable type should be allowed in a model, as it is in Pydantic, just not persisted to the database. I looked at various suggestions for how to do that, and #147 recommended adding a subclass (Tool from BaseTool) that has the private field, and then casting the instance to the superclass when persisting to a DB. However, the error here happens when initializing the model definition, not when trying to save the model. It is likely that #472 (a small change that adds support for Pydantic PrivateAttributes) might be able to help fix this

Operating System

Linux

Operating System Details

Ubuntu 22.04.1 LTS, Linux 5.15.0-25-generic #25-Ubuntu SMP x86_64 GNU/Linux

SQLModel Version

0.0.8

Python Version

Python 3.11.3

Additional Context

No response