Get list item by attribute in Python

Question

I need to load a list of database row objects into memory, and then grab one of those rows by its unique ID. Is there a clean, pythonic way of finding an single object from a list by an attribute value? Or do I just loop and compare?

Is there a reason to not doing this directly with a database query? — Avaris, Feb 01 '12 at 00:45

score 23 · Accepted Answer · answered Feb 01 '12 at 00:21

Yes, you loop and compare:

items = [item for item in container if item.attribute == value]

And you get back a list which can be tested to see how many you found.

If you will be doing this a lot, consider using a dictionary, where the key is the attribute you're interested in.

score 19 · Answer 2 · edited May 23 '17 at 12:10

19

If you do this it only gives the very first match, instead of comparing the whole list: find first sequence item that matches a criterion.

If you do something like this, you don't have to catch the exception but get None instead:

item = next((i for i in items if i == 'value'), None)

edited May 23 '17 at 12:10

Community

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answered Sep 03 '13 at 07:31

Ruud Althuizen

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Chris Cooper · Answer 3 · 2012-02-01T00:31:12.363

7

You can filter:

matches = filter(lambda obj: obj.attribute == "target value", myListOfObjects)

Refer to kindall's answer for advice on efficiency. If you're doing this a lot, it's not the right way.

edited Feb 01 '12 at 00:31

answered Feb 01 '12 at 00:20

Chris Cooper

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what would be the right way to do so efficiently? Thanks. – moeseth Apr 12 '16 at 19:28

Get list item by attribute in Python

3 Answers3