CODEWITHSUNDEEP
python
Daniel F
Daniel F

Reputation: 14399

Finding substring in list of strings, return index

I've got a list of strings dumped by readlines() and I want to find the index of the first line that includes a substring, or the last line.

This works, but seems clunky:

fooIndex=listOfStrings.index((next((x for x in listOfStrings if "foo" in x),listOfStrings[-1])))

There has to be a better way than searching twice, but I can't find it.

Upvotes: 3

Views: 4566

Answers (2)

tobias_k
tobias_k

Reputation: 82949

I don't think there is a good (i.e. readable) one-line solution for this. Alternatively to @eugene's loop, you could also use a try/except.

def get_index(list_of_strings, substring):
    try:
        return next(i for i, e in enumerate(list_of_strings) if substring in e)
    except StopIteration:
        return len(list_of_strings) - 1

The code is a little longer, but IMHO the intent is very clear: Try to get the next index that contains the substring, or the length of the list minus one.

Update: In fact, there is a good (well, somewhat okay-ish) one-liner, and you almost had it, using the default parameter of next, but instead of using the last element itself as default, and then calling index, just put the index itself and combine with enumerate:

next((i for i, e in enumerate(list_of_strings) if substring in e), 
     len(list_of_strings) - 1)

Upvotes: 3

Eugene Yarmash
Eugene Yarmash

Reputation: 150128

Using enumerate() in a function would be both more readable and efficient:

def get_index(strings, substr):
    for idx, string in enumerate(strings):
        if substr in string:
            break
    return idx

Note that you don't need to call .readlines() on a file object to iterate over the lines — just use it as an iterable.

Upvotes: 2

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