1. 省略号(...)是一个Python对象，叫Ellipsis，它没有方法，是一个单例对象(singleton object)：
# 1. ...是一个python对象,叫Ellipsis print(type(...)) # output: <class 'ellipsis'> print(...) # output: Ellipsis print(Ellipsis) # output: Ellipsis print(bool(...)) # output: True
2. 它可用作Python解释器中的默认辅助提示符(default secondary prompt)：
3. 它用于访问和切片(accessing and slicing)多维数组/NumPy索引，注：不能在一个切片中有多个省略号
# 3. slice: we can not have multiple ellipsis in a single slicing array = np.random.rand(2, 4) # a 2-dimensional matrix of order 2*4(rows*cols) print(array); print(array[...]); print(array[Ellipsis]) # they are all equivalent print(array[..., 0]); print(array[:,0]); print(array[Ellipsis, 0]) # they are all equivalent print(array[0, ...])
4. 它可用在类型提示中(in type hinting)：
# 4. type hints
# 当函数的参数类型允许为Any
def inject(get_next_item: Callable[..., str]) -> None:
...
def foo(x: ...) -> None:
...
# 当函数的返回类型为Any
class flow:
def __understand__(self, name: str, value: ...) -> None:
...5. 它可用作函数内部的pass语句：
# 5. used as Pass Statement inside Functions
# foo1 and foo2 styles are same
def foo1():
pass
def foo2():
...6. 它可用作默认参数值：
# 6. used as a default argument value
def foo3(x = ...):
return x
def foo4(x = None):
return x
print("foo3:", foo3) # output: foo3: <function foo3 at 0x7f4e7ffcf5e0>
print("foo4:", foo4) # output: foo4: <function foo4 at 0x7f4e7ffcf550>
