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What is the easiest way to search through a list of dicts in Python?

Answer 1

+2 A:

You can flatten it with a list comprehension and use in:

id in [d['id'] for d in id_list]

You can also use generator expressions, which have different performance characteristics (and will use less memory if your list is huge):

id in (d['id'] for d in id_list)

Nathon 2010-10-13 13:54:23

Thanks, which of these is more efficient?

ensnare 2010-10-13 13:58:05

@ensnare: The second one, it will stop as soon as it finds the id. However, if you are going to do this often, put all ids into a set: `ids = set(d['id'] for d in id_list)` and then just check whether `givenId in ids`

eumiro 2010-10-13 14:00:18

This was really helpful. Thank you.

ensnare 2010-10-13 14:05:17

I explicitly left out the most efficient thing I could think of (which, in retrospect, is less efficient than @eumiro's set solution) because it's rather obfuscated and involves dicts and the question was "easiest". That said, I'm not convinced that the generator expression is most efficient in all cases. Certainly in this one, but if you're storing it and searching it repeatedly and it matters, you'd be better off measuring.

Nathon 2010-10-13 14:07:09

Answer 2

+6 A:

Here's a one-liner:

if some_id in [d.get('id') for d in id_list]:
    pass

Not very efficient though.

edit -- A better approach might be:

if some_id in (d.get('id') for d in id_list):
    pass

This way, the list isn't generated in full length beforehand.

Santiago Lezica 2010-10-13 13:55:51

Answer 3

+4 A:

if you make a dictionary of your search id,

search_dic = {'id': '0c871320cf5111df87da000c29196d3d'}

id_list = ({'id': '0c871320cf5111df87da000c29196d3d'}, 
           {'id': '2eeeb9f4cf5111df87da000c29196d3d'}, 
           {'id': '3b982384cf5111df87da000c29196d3d'}, 
           {'id': '3f6f3fcecf5111df87da000c29196d3d'}, 
           {'id': '44762370cf5111df87da000c29196d3d'}, 
           {'id': '4ba0d294cf5111df87da000c29196d3d'})


if search_dic in id_list:
    print 'yes'

joaquin 2010-10-13 13:59:47

This was really helpful. Thank you.

ensnare 2010-10-13 14:06:18

Answer 4

+3 A:

any(x.get('id')==given_id for x in id_list)

. . . returns boolean. Efficiency? See S.Lott's answer

mshsayem 2010-10-13 14:13:19

Answer 5

+5 A:

How can I easily check if a given id is in this list or not?

Make a set

keys = set( d['id'] for d in id_list )
if some_value in keys

Don't ask if this is "efficient" or "best". It involves the standard tradeoff.

Building the set takes time. But the lookup is then instant.

If you do a lot of lookups, the cost of building the set is amortized over each lookup.
If you do few lookups, the cost of building the set may be higher than something ilike {'id':some_value} in id_list.

S.Lott 2010-10-13 14:19:38

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What is the easiest way to search through a list of dicts in Python?

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