```Python
from typing import Union
from fastapi import Cookie, FastAPI, Header, Path, Query

app = FastAPI()


@app.get("/items/{item_id}")
def main(
    item_id: int = Path(gt=0),
    query: Union[str, None] = Query(default=None, max_length=10),
    session: Union[str, None] = Cookie(default=None, min_length=3),

c,d,e,f=[],g=0,h=a.length;h>g;g++)d=a[g],d.style&&(f[g]=L.get(d,"olddisplay"),c=d.style.display,b?(f[g]||"none"!==c||(d.style.display=""),""===d.style.display&&S(d)&&(f[g]=L.access(d,"olddisplay",tb(d.nodeName)))):(e=S(d),"none"===c&&e||L.set(d,"olddisplay",e?c:n.css(d,"display"))));for(g=0;h>g;g++)d=a[g],d.style&&(b&&"none"!==d.style.display&&""!==d.style.display||(d.style.display=b?f[g]||"":"none"));return a}n.extend({cssHooks:{opacity:{get:function(a,b){if(b){var c=xb(a,"opacity");return""===c?"1...

Path-параметр всегда является обязательным, поскольку он составляет часть пути.

Поэтому следует объявить его с помощью `...`, чтобы обозначить, что этот параметр обязательный.

Тем не менее, даже если вы объявите его как `None` или установите для него значение по умолчанию, это ни на что не повлияет и параметр останется обязательным.

///

## Задайте нужный вам порядок параметров

/// tip | "Подсказка"

可在一个*路径操作*中声明多个 `File` 和 `Form` 参数，但不能同时声明要接收 JSON 的 `Body` 字段。因为此时请求体的编码是 `multipart/form-data`，不是 `application/json`。

这不是 **FastAPI** 的问题，而是 HTTP 协议的规定。

///

## 可选文件上传

您可以通过使用标准类型注解并将 None 作为默认值的方式将一个文件参数设为可选:

//// tab | Python 3.9+

```Python hl_lines="7  14"
{!> ../../docs_src/request_files/tutorial001_02_py310.py!}
```

////

//// tab | Python 3.8+

// If an error is returned no goroutines have been started and r.err will have been set.
func (r *Reader) startReaders(newReader func(io.Reader) *csv.Reader) error {
	if r.args.FileHeaderInfo != none {
		// Read column names
		// Get one line.
		b, err := r.nextSplit(0, nil)
		if err != nil {
			r.err = err
			return err
		}
		if !utf8.Valid(b) {
			return errInvalidTextEncodingError()
		}

```

If the error type is `*RemoteErr`, then the error was returned by the remote server. Otherwise it is a local error.

Context timeouts are propagated, and a default timeout of 1 minute is added if none is specified.

There is no cancellation propagation for single payload requests.
When the context is canceled, the request will return at once with an appropriate error. 

	testGenerateOption(t, false, func(t *testing.T, actual, expected []admitv1.MutatingWebhook) {
		if err := assert.Compare(actual, expected); err == nil {
			t.Errorf("expected diff between webhooks, got none")
		}
	})

  // that are not part of the Kubernetes system.
  // +optional
  repeated string externalIPs = 5;

  // Supports "ClientIP" and "None". Used to maintain session affinity.
  // Enable client IP based session affinity.
  // Must be ClientIP or None.
  // Defaults to None.
  // More info: https://kubernetes.io/docs/concepts/services-networking/service/#virtual-ips-and-service-proxies
  // +optional

				CheckUser(t, models3[idx], user)
			})
		}
	}

	var none []User
	if err := DB.Where("name in (?)", []string{}).Find(&none).Error; err != nil || len(none) != 0 {
		t.Errorf("errors happened when query find with in clause and zero length parameter: %v, length: %v", err, len(none))
	}
}

func TestQueryWithAssociation(t *testing.T) {

    val cookieBuilder =
      Cookie.Builder()
        .name("a")
        .value("b")
        .domain("example.com")
        .sameSite("None")

    val cookie = cookieBuilder.build()
    assertThat(cookie.sameSite).isEqualTo("None")
  }

  @Test fun equalsAndHashCode() {
    val cookieStrings =
      Arrays.asList(
        "a=b; Path=/c; Domain=example.com; Max-Age=5; Secure; HttpOnly",