检查列表索引是否存在

Question

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

Other than:

1. using len(list)

2. using

    try: ... except IndexError: ... 

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

Answer 1

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

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.

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.

Answer 2

You could use list comprehensions.

index in [someList.index(item) for item in someList]:

This will return true if there are at least index items in the list.

For dictionaries you could do something similar:

index in [someDictionary.keys().index(item) for item in someDictionary.keys()]

It's worth pointing out that this really is a moot point since using len(list) or try ... except works perfectly well. But hey, you asked for another way, so here's another way.