Python Ellipsis的使用实战

print(Ellipsis)  # 输出: ...
print(type(Ellipsis))  # 输出: <class 'ellipsis'>
print(Ellipsis is ...)  # 输出: True

a = ...
b = Ellipsis
print(a is b)  # 输出: True

import numpy as np

arr = np.array([
    [[1, 2], [3, 4]],
    [[5, 6], [7, 8]]
])  # 形状: (2, 2, 2)

# 等效操作
print(arr[0, ...])  # 等价于 arr[0, :, :]
print(arr[..., 0])  # 等价于 arr[:, :, 0]

from typing import Callable

# 表示接受任意参数并返回 int 的函数
def func(callback: Callable[..., int]) -> None:
    result = callback(1, 2, 3)  # 回调函数可接受任意参数
    print(result)

def todo_function():
    ...  # 等价于 pass，但更明确表示“待实现”

# 等效于
def todo_function():
    pass

class MyData:
    def __getitem__(self, key):
        if key is Ellipsis:
            return "处理所有数据"
        return f"处理 {key}"

data = MyData()
print(data[...])  # 输出: 处理所有数据
print(data[1])    # 输出: 处理 1

from typing import overload

@overload
def process_data(data: int) -> int: ...
@overload
def process_data(data: str) -> str: ...

def process_data(data):
    if isinstance(data, int):
        return data * 2
    return data.upper()

from typing import AsyncGenerator

async def async_generator() -> AsyncGenerator[int, ...]:
    for i in range(3):
        yield i
        await asyncio.sleep(1)

class Config:
    def __get__(self, instance, owner):
        if instance is None:
            return self
        return instance._config.get(self.name, ...)  # 使用 Ellipsis 表示默认值

    def __set_name__(self, owner, name):
        self.name = name

# 错误示例：用 None 代替 Ellipsis 进行 NumPy 切片
arr = np.array([1, 2, 3])
try:
    arr[None]  # 这里 None 表示新增维度，而非 Ellipsis 的含义
except:
    pass

# 正确示例
arr[...]  # 获取整个数组

my_list = [1, 2, 3, 4]
try:
    my_list[...]  # 报错：TypeError
except TypeError:
    arr = np.array(my_list)
    print(arr[...])  # 输出: [1 2 3 4]

def func(param=None):
    if param is None:
        # 处理默认情况
        pass
    else:
        # 处理传入值
        pass