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[BUG] Dependencies imported from file with python annotations don't work

See original GitHub issue

Describe the bug

When there is a file that contains python annotations import at the top and contains some async function returning parameters dependency injection doesn’t work.

To Reproduce

Create file deps.py:

from __future__ import annotation

async def test(foo: Optional[str] = None):
  return foo

And then in the other file containing route definition:

from .deps import test

@api.get("/foo")
async def foo_route(foo: Optional[str] = Depends(test)):
  return None

Trying to run the app with such configuration results in error:

...
  File "/Users/user/.local/share/virtualenvs/pilgrim-api-A9HJbenQ/lib/python3.7/site-packages/fastapi/dependencies/utils.py", line 179, in get_dependant
    param_field = get_param_field(param=param, default_schema=params.Query)
  File "/Users/user/.local/share/virtualenvs/pilgrim-api-A9HJbenQ/lib/python3.7/site-packages/fastapi/dependencies/utils.py", line 265, in get_param_field
    schema=schema,
  File "/Users/user/.local/share/virtualenvs/pilgrim-api-A9HJbenQ/lib/python3.7/site-packages/pydantic/fields.py", line 112, in __init__
    self.prepare()
  File "/Users/user/.local/share/virtualenvs/pilgrim-api-A9HJbenQ/lib/python3.7/site-packages/pydantic/fields.py", line 178, in prepare
    self._populate_validators()
  File "/Users/user/.local/share/virtualenvs/pilgrim-api-A9HJbenQ/lib/python3.7/site-packages/pydantic/fields.py", line 269, in _populate_validators
    *(get_validators() if get_validators else list(find_validators(self.type_, self.model_config))),
  File "/Users/user/.local/share/virtualenvs/pilgrim-api-A9HJbenQ/lib/python3.7/site-packages/pydantic/validators.py", line 470, in find_validators
    raise RuntimeError(f'error checking inheritance of {type_!r} (type: {display_as_type(type_)})') from e
RuntimeError: error checking inheritance of 'Optional[str]' (type: str)

Expected behavior It runs and works.

Environment:

OS: macOS
FastAPI Version: 0.35
Python: 3.7.3

Issue Analytics

State:
Created 4 years ago
Comments:6 (4 by maintainers)

Top GitHub Comments

1reaction

dmontagucommented, Aug 19, 2019

I don’t know if this is the ultimate source of the error, but FastAPI has some issues with from __future__ import annotations (and string-annotations in general), and I’ve seen it cause the specific error message you are receiving before. Try removing the future import and see if it fixes the problem?

0reactions

tiangolocommented, Apr 10, 2020

Thanks for the help here everyone! 👏 🙇

Thanks for reporting back and closing the issue @LKay 👍