Python3中省略号(...)用法介绍
fengbingchun 人气:01. 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>
加载全部内容