Querying all dictionaries in a python list

Question

Without using loops to iterate through a list, is there a preferred syntax for retrieving a value of a given key from all dictionaries in a list?

This is a loop which achieves what I need:

>>> my_list = [{'foo':'bar'},{'foo':'buzz'}]
>>> [x['foo'] for x in my_list]
['bar', 'buzz']

This is intuitively how I think the same result should be achieved:

>>> my_list = [{'foo':'bar'},{'foo':'buzz'}]
>>> [my_list[*]['foo']]
['bar', 'buzz']

What's wrong with looping though the list? No, standard lists don't have that kind of magic syntax. — deceze, Jan 20 '21 at 14:28
But... in the end you're looping the list. So what's wrong with having an explicit loop that clearly conveys that instead of some unclear syntax which will just confuse readers? — Tomerikoo, Jan 20 '21 at 14:42
"This is intuitively how I think the same result should be achieved" then write up a PEP proposing this change, but there is no special syntax. For loops are very pythonic — juanpa.arrivillaga, Jan 20 '21 at 15:07

some_programmer · Answer 1 · 2021-01-20T14:40:53.173

1

One way is to use map

mylist = [{'foo':'bar'},{'foo':'buzz'}]

def extract(x):
    return x['foo']

a = list(map(extract, mylist))

print(a)
# ['bar', 'buzz']

Or as suggested by deceze in the comments: operator.itemgetter

from operator import itemgetter

mylist = [{'foo':'bar'},{'foo':'buzz'}]
a = list(map(itemgetter('foo'), mylist))
print(a)
# ['bar', 'buzz']

edited Jan 20 '21 at 14:40

answered Jan 20 '21 at 14:32

some_programmer

1

`map(operator.itemgetter('foo'), ...)` would be more elegant… – deceze Jan 20 '21 at 14:35
@deceze Thanks. I never used it, but checked it out now and added that to the solution as well – some_programmer Jan 20 '21 at 14:42
2

Arguably the first method in the question is the most elegant... – Tomerikoo Jan 20 '21 at 14:43
1

I agree. List comprehension is the best – some_programmer Jan 20 '21 at 14:43

score 0 · Answer 2 · answered Jan 20 '21 at 14:47

0

If you don't want any modules, or separate functions,

x = list(map(lambda x: x['foo'], my_list))

print(x)

>>> ['bar', 'buzz']

answered Jan 20 '21 at 14:47

coderoftheday

2 Answers2