Most pythonic way to get one item from a list?

Question

Say I have a list of dicts where dict['id'] is unique, and I want to access one specific dict.

This is how I would usually do that, more or less.

d_ = [d for d in list_of_dicts where d['id']=='the_id_i_want'][0]

Is there a better/cleaner/more pythonic way to do this?

This is an API response, otherwise I'd just make it a dict in the first place.

Or maintain an additional dict mapping id to the list of dicts. — jarmod, Jun 02 '22 at 21:02
If each dict in the list contains uinque ids, why not combine them into a single dict — Ach113, Jun 02 '22 at 21:03
Use a regular `for` loop and break out of the loop when you find the matching dict. — Barmar, Jun 02 '22 at 21:06
Is this a one time thing or is it done often with the same data? If often, the cost of indexing the list would be worth it. — tdelaney, Jun 02 '22 at 22:00
Just use a regular for loop and break out early. For loops are perfectly pythonic — juanpa.arrivillaga, Jun 02 '22 at 22:02

score 3 · Answer 1 · answered Jun 02 '22 at 21:07

3

Just use an ordinary for loop. Then you can stop the loop when you find the one you want. The list comprehension will keep looping unnecessarily.

d_ = None
for d in list_of_dicts:
    if d['id'] == 'the_id_i_want':
        d_ = d
        break

answered Jun 02 '22 at 21:07

Barmar

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score 3 · Answer 2 · answered Jun 02 '22 at 21:10

3

You can use next() (Note: you can use default= parameter to specify value to return when dict is not found):

list_of_dicts = [{"id": 3}, {"id": 4}, {"id": 1}]

d = next(d for d in list_of_dicts if d["id"] == 1)
print(d)

Prints:

{'id': 1}

answered Jun 02 '22 at 21:10

Andrej Kesely

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score 3 · Answer 3 · edited Jun 02 '22 at 21:12

3

You can avoid looping over the entire list using a generator to take just the leading value:

d = next( 
    (d for d in list_of_dicts if d['id'] == 'the_id_i_want'), 
    None)

Here, if it is not found, d will be set to None.

edited Jun 02 '22 at 21:12

Chris

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answered Jun 02 '22 at 21:10

donkopotamus

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score 0 · Answer 4 · answered Jun 02 '22 at 21:14

Create a dict with indices of the unique id, then use that to select the dict you want

d = [{"id": 1, "val": 2}, {"id": 2, "val": 2}]
inds = {x["id"]: i for i, x in enumerate(d)}

# if you want dict with id equal to 1
d[inds[1]]
# {'id': 1, 'val': 2}

Most pythonic way to get one item from a list?

4 Answers4