{* ../../docs_src/query_params/tutorial002_py310.py hl[7] *}

In this case, the function parameter `q` will be optional, and will be `None` by default.

/// check

Also notice that **FastAPI** is smart enough to notice that the path parameter `item_id` is a path parameter and `q` is not, so, it's a query parameter.

///

## Query parameter type conversion { #query-parameter-type-conversion }

第一个值是默认值，还可以传递所有验证参数或注释参数：


{* ../../docs_src/cookie_params/tutorial001_an_py310.py hl[9] *}

/// note | 技术细节

`Cookie` 、`Path` 、`Query` 是**兄弟类**，都继承自共用的 `Param` 类。

注意，从 `fastapi` 导入的 `Query`、`Path`、`Cookie` 等对象，实际上是返回特殊类的函数。

///

/// info | 说明

必须使用 `Cookie` 声明 cookie 参数，否则该参数会被解释为查询参数。

///

## 小结

from fastapi.testclient import TestClient

from docs_src.configure_swagger_ui.tutorial001_py39 import app

client = TestClient(app)


def test_swagger_ui():
    response = client.get("/docs")
    assert response.status_code == 200, response.text
    assert '"syntaxHighlight": false' in response.text, (
        "syntaxHighlight should be included and converted to JSON"
    )
    assert '"dom_id": "#swagger-ui"' in response.text, (

from fastapi.testclient import TestClient

from docs_src.metadata.tutorial001_1_py39 import app

client = TestClient(app)


def test_items():
    response = client.get("/items/")
    assert response.status_code == 200, response.text
    assert response.json() == [{"name": "Katana"}]


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text

import os
from typing import Any

from pdm.backend.hooks import Context

TIANGOLO_BUILD_PACKAGE = os.getenv("TIANGOLO_BUILD_PACKAGE", "fastapi")


def pdm_build_initialize(context: Context) -> None:
    metadata = context.config.metadata
    # Get custom config for the current package, from the env var
    config: dict[str, Any] = context.config.data["tool"]["tiangolo"][
        "_internal-slim-build"
    ]["packages"].get(TIANGOLO_BUILD_PACKAGE)

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

## Use cases { #use-cases }

Some use cases include:

from fastapi.testclient import TestClient

from docs_src.cors.tutorial001_py39 import app


def test_cors():
    client = TestClient(app)
    # Test pre-flight response
    headers = {
        "Origin": "https://localhost.tiangolo.com",
        "Access-Control-Request-Method": "GET",
        "Access-Control-Request-Headers": "X-Example",
    }
    response = client.options("/", headers=headers)

import os
from pathlib import Path

import pytest
from fastapi.testclient import TestClient


@pytest.fixture(scope="module")
def client():
    static_dir: Path = Path(os.getcwd()) / "static"
    print(static_dir)
    static_dir.mkdir(exist_ok=True)
    from docs_src.custom_docs_ui.tutorial002_py39 import app

    with TestClient(app) as client:
        yield client
    static_dir.rmdir()

import importlib

import pytest
from fastapi.testclient import TestClient
from pytest import MonkeyPatch


@pytest.fixture(name="app", params=[pytest.param("tutorial001_py39")])
def get_app(request: pytest.FixtureRequest, monkeypatch: MonkeyPatch):
    monkeypatch.setenv("ADMIN_EMAIL", "******@****.***")
    mod = importlib.import_module(f"docs_src.settings.{request.param}")
    return mod.app


def test_settings(app):

from fastapi.testclient import TestClient

from docs_src.metadata.tutorial001_py39 import app

client = TestClient(app)


def test_items():
    response = client.get("/items/")
    assert response.status_code == 200, response.text
    assert response.json() == [{"name": "Katana"}]


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {