Python:单冒号与双冒号 [英] Python: single colon vs double colon

问题描述

在这种情况下，单冒号和双冒号有什么区别? data[0:,4]与data[0::,4]

What is the difference between single and double colon in this situation? data[0:,4] vs data[0::,4]

women_only_stats = data[0::,4] == "female" 

men_only_stats = data[0::,4] != "female"   

我尝试将data[0::,4]替换为data[0:,4]，但没有区别.在这种情况或其他情况下有什么区别吗?

I tried to replace data[0::,4] with data[0:,4] and I see no difference. Is there any difference in this or another case?

data是具有像['1' '0' '3' 'Braund, Mr. Owen Harris' 'male' '22' '1' '0' 'A/5 21171' '7.25' '' 'S']

推荐答案

否，没有区别.

请参阅Python文档中的切片:

See the Python documentation for slice:

从文档中:a[start:stop:step]

start和step参数默认为None.切片对象有 只读数据属性start，stop和step，它们仅返回 参数值(或其默认值).

The start and step arguments default to None. Slice objects have read-only data attributes start, stop and step which merely return the argument values (or their default).

在这种情况下，您要包含一个空的step参数.

In this case, you are including an empty step parameter.

>>> a = [1,2,3,4]
>>> a[2:]
[3,4]
>>> a[2::]
[3,4]
>>> a[2:] == a[2::]
True

并了解step参数的实际作用:

And to understand what the step parameter actually does:

>>> b = [1,2,3,4,5,6,7,8,9,10]
>>> b[0::5]
[1, 6]
>>> b[1::5]
[2, 7]

因此，通过将其保留为隐式None(即通过a[2:]或a[2::])，您将不会以任何方式更改代码的输出.

So by leaving it to be implicitly None (i.e., by either a[2:] or a[2::]), you are not going to change the output of your code in any way.

希望这会有所帮助.

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