Unions in response_models result in incorrect casting

[turettn]

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Example Code

from typing import Union
from fastapi import FastAPI
from fastapi.testclient import TestClient

APP = FastAPI()
TESTER = TestClient(APP)

@APP.get('/', response_model=Union[int, bool])
def root():
    return True

def test_root():
    resp = TESTER.get("/")
    assert resp.status_code == 200
    assert resp.json() is True

"""
The test fails with:

    def test_root():
        resp = TESTER.get("/")
        assert resp.status_code == 200
>       assert resp.json() is True
E       assert 1 is True
E        +  where 1 = <bound method Response.json of <Response [200]>>()
E        +    where <bound method Response.json of <Response [200]>> = <Response [200]>.json
"""

Description

If response-model is set to Union[int, bool], and return a bool, the result is cast to an int.

I expect it to return a bool.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.70.0

Python Version

3.7.10

Additional Context

No response

[uriyyo]

pydantic tries to convert values to destination type when it's possible.

The solution will be to use pydantic StrictInt and StrictBool:

from typing import Union
from fastapi import FastAPI
from fastapi.testclient import TestClient
from pydantic import StrictInt, StrictBool

APP = FastAPI()
TESTER = TestClient(APP)


@APP.get('/', response_model=Union[StrictInt, StrictBool])
def root():
    return 1


def test_root():
    resp = TESTER.get("/")
    assert resp.status_code == 200
    assert resp.json() is True

More info about pydantic:
data conversion - https://pydantic-docs.helpmanual.io/usage/models/#data-conversion
strict types - https://pydantic-docs.helpmanual.io/usage/types/#strict-types

[turettn]

@uriyyo Thank you! I tried to search through the pydantic docs but couldn't find this. That's perfect.