检查列表索引是否存在 [英] To check whether index of list exists

问题描述

有什么办法可以检查列表的索引是否存在?

Is there any solution to check whether index of list exists?

除:

1. 使用len(list)

使用

try:
   ...
except IndexError:
   ...

由于dict有一个dict.has_key(key)来检查键是否存在，是否有任何方法可以检查列表的索引?

As dict has a dict.has_key(key) to check whether key exists, is there any method to check index for list?

推荐答案

不，没有其他方法可以测试索引是否存在.

No, there are no additional methods to test if an index exists.

字典键不容易预测；您必须进行成员资格测试，以确定某个键是否有效存在，因为扫描所有键的效率很低.

Dictionary keys are not easily predicted; you have to have a membership test to determine if a key exists efficiently, as scanning through all keys would be inefficient.

列表不存在该问题； len(somelist)很便宜(长度缓存在列表对象上)，所以index < len(somelist)是 测试索引是否存在的方法，如果您期望索引是大部分时间都在列表边界内.

Lists do not suffer from that problem; len(somelist) is cheap (the length is cached on the list object), so index < len(somelist) is the way to test if an index exists, with exception handling a great fallback if you expect the index to be within the list boundaries most of the time.

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