Updating a list of python dictionaries with a key, value pair from another list

Question

Let's say I have the following list of python dictionary:

dict1 = [{'domain':'Ratios'},{'domain':'Geometry'}]

and a list like:

list1 = [3, 6]

I'd like to update dict1 or create another list as follows:

dict1 = [{'domain':'Ratios', 'count':3}, {'domain':'Geometry', 'count':6}]

How would I do this?

According to the example, the title to this question should be: "Updating a list of python dictionaries values from another list". From the current title I would expect that list1 = [('Ratios', 3), ('Geometry', 6)] — yucer, Dec 12 '16 at 09:20

jamylak · Accepted Answer · 2015-03-05T05:24:26.370

23

>>> l1 = [{'domain':'Ratios'},{'domain':'Geometry'}]
>>> l2 = [3, 6]
>>> for d,num in zip(l1,l2):
        d['count'] = num


>>> l1
[{'count': 3, 'domain': 'Ratios'}, {'count': 6, 'domain': 'Geometry'}]

Another way of doing it, this time with a list comprehension which does not mutate the original:

>>> [dict(d, count=n) for d, n in zip(l1, l2)]
[{'count': 3, 'domain': 'Ratios'}, {'count': 6, 'domain': 'Geometry'}]

edited Mar 05 '15 at 05:24

answered May 15 '12 at 00:23

jamylak

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Thanks. The second solution yields an error in its current form – Harshil Parikh May 15 '12 at 02:32
Are you using python 3? I will probably change it to be cross compatible. – jamylak May 15 '12 at 02:33
which is faster computationally? – amc Nov 06 '17 at 18:56
@amc It's probably not worth worrying about :P But could run some `timeit`s on it – jamylak Nov 06 '17 at 22:48

score 6 · Answer 2 · edited May 15 '12 at 00:41

6

You could do this:

for i, d in enumerate(dict1):
    d['count'] = list1[i]

edited May 15 '12 at 00:41

jamylak

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answered May 15 '12 at 00:22

larsks

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Thanasis Petsas · Answer 3 · 2012-05-15T00:50:30.903

3

You can do this:

# list index
l_index=0

# iterate over all dictionary objects in dict1 list
for d in dict1:

    # add a field "count" to each dictionary object with
    # the appropriate value from the list
    d["count"]=list1[l_index]

    # increase list index by one
    l_index+=1

This solution doesn't create a new list. Instead, it updates the existing dict1 list.

edited May 15 '12 at 00:50

answered May 15 '12 at 00:41

Thanasis Petsas

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Very verbose for Python but explains everything really well. – jamylak May 15 '12 at 00:42
1

Yes you have right! It is very verbose. But since there are other answers less verbose here, I think it would be ok to add a more explanatory solution.. – Thanasis Petsas May 15 '12 at 00:44

score 0 · Answer 4 · edited May 15 '12 at 21:28

0

Using list comprehension will be the pythonic way to do it.

[data.update({'count': list1[index]}) for index, data in enumerate(dict1)]

The dict1 will be updated with the corresponding value from list1.

edited May 15 '12 at 21:28

Jason Sundram

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answered May 15 '12 at 18:25

dan-boa

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-1 Using a list comprehension for mutations is **not** pythonic. Use a simple for loop. – jamylak Aug 07 '12 at 08:14
update on a dict work on reference not provide output . data.update() return None. You will get out put as [None, None, ....] – Manoj Sahu Mar 01 '16 at 07:51

Updating a list of python dictionaries with a key, value pair from another list

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