Unnecessary Union for Same-Type Sequence Members

[michaeligreenberg]

Here's an example FastAPI app:

from typing import Tuple

from fastapi import FastAPI
from pydantic import BaseModel

class Point(BaseModel):
    coordinates: Tuple[float, float]

app = FastAPI()

@app.post("/point")
def create_trip(point: Point):
    return {"status": "OK"}

Using datamodel-codegen with the --use-generic-container-types option on the response from the app's /openapi.json endpoint produces the following schema:

from __future__ import annotations

from typing import Optional, Sequence, Union

from pydantic import BaseModel, Field


class Point(BaseModel):
    coordinates: Sequence[Union[float, float]] = Field(
        ..., max_items=2, min_items=2, title='Coordinates'
    )

...

Besides the Pydantic v1 problem of unenforced field constraints on a generic, I also noticed that the coordinates field has the repetitive generic type of Sequence[Union[float, float]]; I believe that just Sequence[float] would suffice. A possible improvement would be to detect when there is only one possible type and omit the Union.

Details
fastapi 0.95.0
datamodel-codegen 0.17.1