# Python 类型提示简介

**Python 3.6+ 版本**加入了对"类型提示"的支持。

这些**"类型提示"**是一种新的语法（在 Python 3.6 版本加入）用来声明一个变量的<abbr title="例如：str、int、float、bool">类型</abbr>。

通过声明变量的类型，编辑器和一些工具能给你提供更好的支持。

这只是一个关于 Python 类型提示的**快速入门 / 复习**。它仅涵盖与 **FastAPI** 一起使用所需的最少部分...实际上只有很少一点。

整个 **FastAPI** 都基于这些类型提示构建，它们带来了许多优点和好处。

但即使你不会用到 **FastAPI**，了解一下类型提示也会让你从中受益。

/// note

如果你已经精通 Python，并且了解关于类型提示的一切知识，直接跳到下一章节吧。

///

## 动机

让我们从一个简单的例子开始：

    price: float = Field(examples=[35.4])
    tax: float | None = Field(default=None, examples=[3.2])


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item):
    results = {"item_id": item_id, "item": item}

from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/users/{user_id}/items/{item_id}")
async def read_user_item(
    user_id: int, item_id: str, q: Union[str, None] = None, short: bool = False
):
    item = {"item_id": item_id, "owner_id": user_id}
    if q:
        item.update({"q": q})
    if not short:
        item.update(

    assert response.status_code == 200, response.text
    assert response.text == "x" * 4000
    assert response.headers["Content-Encoding"] == "gzip"
    assert int(response.headers["Content-Length"]) < 4000
    response = client.get("/")

        assertThat(codePoint and 0x7f).isEqualTo(codePoint)
      }
    }

    // Confirm the sections are increasing.
    val rangesIndices = mutableListOf<Int>()
    val rangesOffsets = mutableListOf<Int>()
    for (i in 0 until compactTable.sections.length step 4) {
      rangesIndices += compactTable.sections.read14BitInt(i)
      rangesOffsets += compactTable.sections.read14BitInt(i + 2)
    }

		t.Fatalf("Count should work, but got err %v", err)
	}

	expects := []User{{Name: "main"}, {Name: "other"}, {Name: "other"}}
	sort.SliceStable(users, func(i, j int) bool {
		return strings.Compare(users[i].Name, users[j].Name) < 0
	})

	AssertEqual(t, users, expects)

	var count7 int64

                  @Override
                  protected Collection<String> create(String[] elements) {
                    List<Integer> rowKeys = new ArrayList<>();
                    for (int i = 0; i < elements.length; i++) {
                      rowKeys.add(i);
                    }
                    Table<Integer, Character, String> table =

app = FastAPI()


class BaseItem(BaseModel):
    description: str
    type: str


class CarItem(BaseItem):
    type: str = "car"


class PlaneItem(BaseItem):
    type: str = "plane"
    size: int


items = {
    "item1": {"description": "All my friends drive a low rider", "type": "car"},
    "item2": {
        "description": "Music is my aeroplane, it's my aeroplane",
        "type": "plane",

class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Annotated[
        Item,
        Body(
            examples=[
                {
                    "name": "Foo",
                    "description": "A very nice Item",
                    "price": 35.4,

    price: float
    tax: Union[float, None] = None
    tags: set[str] = set()
    images: Union[list[Image], None] = None


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item):
    results = {"item_id": item_id, "item": item}