# 進階 Python 型別 { #advanced-python-types }

以下是一些在使用 Python 型別時可能有用的額外想法。

## 使用 `Union` 或 `Optional` { #using-union-or-optional }

如果你的程式碼因某些原因無法使用 `|`，例如不是在型別註記中，而是在像 `response_model=` 之類的參數位置，那麼你可以用 `typing` 中的 `Union` 來取代豎線（`|`）。

例如，你可以宣告某個值可以是 `str` 或 `None`：

```python
from typing import Union


def say_hi(name: Union[str, None]):
        print(f"Hi {name}!")
```

在 `typing` 中也有用 `Optional` 宣告某個值可以是 `None` 的速記法。

	typedef struct {
		int count;
		[size_is(count)] ShareInfo502 *array;
	} ShareInfoCtr502;

	typedef [switch_type(int)] union {
		[case(0)] ShareInfo0 *info0;
		[case(1)] ShareInfo1 *info1;
		[case(502)] ShareInfo502 *info1;
	} ShareInfo;

	typedef [switch_type(int)] union {
		[case(0)] ShareInfoCtr0 *info0;
		[case(1)] ShareInfoCtr1 *info1;
		[case(502)] ShareInfoCtr502 *info1;
	} ShareCtr;

	[op(0x0f)]

## `Union` 或 `anyOf` { #union-or-anyof }

你可以將回應宣告為多個型別的 `Union`，表示回應可能是其中任一型別。

在 OpenAPI 中會以 `anyOf` 定義。

要達成這點，使用標準的 Python 型別提示 [`typing.Union`](https://docs.python.org/3/library/typing.html#typing.Union)：

/// note

def test_serialize_sequence_value_with_none_first_in_union():
    """Test that serialize_sequence_value handles Union[None, List[...]] correctly."""
    from typing import Union

    from fastapi._compat import v2

    # Use Union[None, list[str]] to ensure None comes first in the union args
    field_info = FieldInfo(annotation=Union[None, list[str]])  # noqa: UP007
    field = v2.ModelField(name="items", field_info=field_info)

	maps.Copy(setCopy, set)
	return setCopy
}

// add - adds TargetID to the set.
func (set TargetIDSet) add(targetID TargetID) {
	set[targetID] = struct{}{}
}

// Union - returns union with given set as new set.
func (set TargetIDSet) Union(sset TargetIDSet) TargetIDSet {
	nset := set.Clone()

	for k := range sset {
		nset.add(k)
	}

	return nset
}

import types
from collections.abc import Callable
from enum import Enum
from typing import Any, TypeVar, Union

from pydantic import BaseModel
from pydantic.main import IncEx as IncEx

DecoratedCallable = TypeVar("DecoratedCallable", bound=Callable[..., Any])
UnionType = getattr(types, "UnionType", Union)
ModelNameMap = dict[type[BaseModel] | type[Enum], str]

	typedef struct {
		int count;
		[size_is(count)] ShareInfo502 *array;
	} ShareInfoCtr502;

	typedef [switch_type(int)] union {
		[case(0)] ShareInfo0 *info0;
		[case(1)] ShareInfo1 *info1;
		[case(502)] ShareInfo502 *info1;
	} ShareInfo;

	typedef [switch_type(int)] union {
		[case(0)] ShareInfoCtr0 *info0;
		[case(1)] ShareInfoCtr1 *info1;
		[case(502)] ShareInfoCtr502 *info1;
	} ShareCtr;

	[op(0x0f)]

# Always check-out / check-in files with LF line endings.
* text=auto eol=lf

hack/verify-flags/known-flags.txt merge=union
test/test_owners.csv merge=union

**/zz_generated.*.go linguist-generated=true
**/types.generated.go linguist-generated=true
**/generated.pb.go linguist-generated=true
**/generated.proto
**/types_swagger_doc_generated.go linguist-generated=true
api/openapi-spec/*.json linguist-generated=true

CHANGELOG.asciidoc  merge=union

# These files contain expected text output, and should not be changed on
# Windows

pkg go/types, method (*TypeParamList) At(int) *TypeParam
pkg go/types, method (*TypeParamList) Len() int
pkg go/types, method (*Union) Len() int
pkg go/types, method (*Union) String() string
pkg go/types, method (*Union) Term(int) *Term
pkg go/types, method (*Union) Underlying() Type
pkg go/types, type ArgumentError struct
pkg go/types, type ArgumentError struct, Err error
pkg go/types, type ArgumentError struct, Index int