当切片索引超出范围时，如何引发IndexError？ [英] How to raise an IndexError when slice indices are out of range?

问题描述

Python文档指出

切片索引被静默截断，落入允许范围

因此切片列表时没有 IndexErrors 上升，无论 start 或 stop 参数：

and therefor no IndexErrors are risen when slicing a list, regardless what start or stop parameters are used:

>>> egg = [1, "foo", list()]
>>> egg[5:10]
[]

由于列表 egg 不包含任何大于 2 的索引， egg [5] 或 egg [10] 调用会引发 IndexError ：

Since the list egg does not contain any indices greater then 2, a egg[5] or egg[10] call would raise an IndexError:

>> egg[5]
Traceback (most recent call last):
IndexError: list index out of range

现在的问题是，当给定的切片索引超出范围时，我们如何提出 IndexError ？

The question is now, how can we raise an IndexError, when both given slice indices are out of range?

推荐答案

在Python 2中，您可以通过这种方式覆盖 __ getslice __ 方法：

In Python 2 you can override __getslice__ method by this way:

class MyList(list):
    def __getslice__(self, i, j):
        len_ = len(self)
        if i > len_ or j > len_:
            raise IndexError('list index out of range')
        return super(MyList, self).__getslice__(i, j)

然后使用您的班级而不是列表：

Then use your class instead of list:

>>> egg = [1, "foo", list()]
>>> egg = MyList(egg)
>>> egg[5:10]
Traceback (most recent call last):
IndexError: list index out of range

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