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mypy: Blueprint type mismatch with `flask.sansio.blueprints.Blueprint`

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难度
5/5
预计耗时
一周以上
新手友好度
35/100
Issue 类型
缺陷
描述清晰度
需要澄清
活跃度
停滞
技术栈
flask, python
领域
backend, developer-experience

调研方向

先从暴露 app.blueprints 的 Quart Blueprint 和 Quart 入口点入手，然后将它们的注解与 Flask 的 sansio Blueprint 定义进行比较。使用提供的最小示例和 mypy --strict，评估 Flask 的类型标注还是 Quart 侧的 cast 更适合解决这一不匹配问题，并在定义完成标准之前考虑对 Quart/Flask 生态系统的影响。

由索引模型根据 Issue 内容生成。

描述

When using Quart's Blueprint, mypy doesn't recognize its inheritance from flask.sansio.blueprints.Blueprint. This causes type errors when accessing blueprints through app.blueprints, which returns the Flask Blueprint type.

Environment

  • Python version: 3.12.7
  • Quart version: 0.20.0

Minimal Reproducible Example

from quart import Quart
from quart.blueprints import Blueprint


app = Quart(__name__)
bp = Blueprint("test", __name__)
app.register_blueprint(bp)

# This works at runtime but fails type check
def process_blueprint(blueprint: Blueprint) -> None:
    print(f"Processing blueprint: {blueprint.name}")

# Type error here - blueprints.values() returns flask.sansio.blueprints.Blueprint
for blueprint in app.blueprints.values():
    process_blueprint(blueprint)  # Error: Expected quart.blueprints.Blueprint, got flask.sansio.blueprints.Blueprint

# Show inferred types
reveal_type(bp)  # Shows quart.blueprints.Blueprint
reveal_type(app.blueprints)  # Shows Dict[str, flask.sansio.blueprints.Blueprint]

Mypy output:

mypy quart_blueprint_mre.py --show-error-codes --strict

quart_blueprint_mre.py:19: error: Argument 1 to "process_blueprint" has incompatible type "flask.sansio.blueprints.Blueprint"; expected "quart.blueprints.Blueprint"  [arg-type]
quart_blueprint_mre.py:22: note: Revealed type is "quart.blueprints.Blueprint"
quart_blueprint_mre.py:23: note: Revealed type is "builtins.dict[builtins.str, flask.sansio.blueprints.Blueprint]"
Found 1 error in 1 file (checked 1 source file)

In my real codebase, I have something like this:

from typing import TypeAlias

from quart import Quart
from quart.blueprints import Blueprint

Scaffold: TypeAlias = Blueprint | Quart


def _inject_routes(app: Scaffold) -> None:
    for endpoint, func in app.view_functions.items():
        if not injected(func):
            wrapped = _make_wrapper(func)
            app.view_functions[endpoint] = wrapped

It can be fixed, of course, with suppression or with adding flask.sansio.blueprints.Blueprint to the type alias, but I guess it's not the best solution.

As I found out, that's because of the more complex hierarchy of the App/Blueprint classes for Quart. So I'm wondering what would be the best way to handle this inheritance in the type system:

  1. Make Flask's sansio layer more generic to support framework extension:
TBlueprint = TypeVar('TBlueprint', bound='Blueprint', covariant=True)
blueprints: Dict[str, TBlueprint]
  1. Or add type casting on Quart's side:
@property
def blueprints(self) -> Dict[str, Blueprint]:
    return cast(Dict[str, Blueprint], super().blueprints)

I'd be happy to submit a PR with either approach once you suggest me which is more appropriate for the Quart/Flask ecosystem.

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