"切片"在Python表达式文档中 [英] "Slicing" in Python Expressions documentation

问题描述

我不明白Python文档的以下部分：

I don't understand the following part of the Python docs:

http://docs.python.org/reference/expressions.html#slicings

这是指列表切片（ x = [1,2,3,4]; x [0：2] ）..？特别是引用省略号的部分。

Is this referring to list slicing ( x=[1,2,3,4]; x[0:2] )..? Particularly the parts referring to ellipsis..

slice_item       ::=  expression | proper_slice | ellipsis

作为表达式的切片项目的转换是该表达式。省略号切片项目的转换是内置的省略号对象。

The conversion of a slice item that is an expression is that expression. The conversion of an ellipsis slice item is the built-in Ellipsis object.

推荐答案

定义简单测试类，只是打印正在传递的内容：

Defining simple test class that just prints what is being passed:

>>> class TestGetitem(object):
...   def __getitem__(self, item):
...     print type(item), item
... 
>>> t = TestGetitem()

表达式示例：

>>> t[1]
<type 'int'> 1
>>> t[3-2]
<type 'int'> 1
>>> t['test']
<type 'str'> test
>>> t[t]
<class '__main__.TestGetitem'> <__main__.TestGetitem object at 0xb7e9bc4c>

切片示例：

>>> t[1:2]
<type 'slice'> slice(1, 2, None)
>>> t[1:'this':t]
<type 'slice'> slice(1, 'this', <__main__.TestGetitem object at 0xb7e9bc4c>)

省略号示例：

>>> t[...]
<type 'ellipsis'> Ellipsis

带省略号和切片的元组：

Tuple with ellipsis and slice:

>>> t[...,1:]
<type 'tuple'> (Ellipsis, slice(1, None, None))

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