How to combine the dictionaries in python

Question

I have 2 dictionaries

dict1 = {'color': {'attri': ['Black']}, 'diameter': {'attri': ['(300, 600)']}}

dict2 = {'size': {'op':'in'}, 'diameter': {'op':'range'}, 'color': {'op':'in'}}

I want to combine the 2 dictionaries such that

dict3 = {'color': {'op': 'in', 'attri': ['Black']}, 'diameter': {'op': 'range', 'attri': ['(300,600)']}}

check this link answer is already there [link](https://stackoverflow.com/questions/38987/how-to-merge-two-dictionaries-in-a-single-expression) — ashish pal, Jun 06 '18 at 09:12

FHTMitchell · Answer 1 · 2021-05-04T14:27:20.303

This method uses a defaultdict and is safe even if a key only appears in one of the dictionaries.

import itertools
import collections

dict3 = collections.defaultdict(dict)

for key, value in itertools.chain(dict1.items(), dict2.items()):
     dict3[key].update(value)

Proof -- applied to:

dict1 = {'color': {'attri':['Black']}, 'diameter': {'attri':['(300, 600)']}}
dict2 = {'size': {'op':'in'}, 'diameter': {'op':'range'}, 'color': {'op':'in'}}

the output of dict(dict3) is:

{'color': {'attri': ['Black'], 'op': 'in'},
'diameter': {'attri': ['(300, 600)'], 'op': 'range'},
'size': {'op': 'in'}}

Although looking at your expected output, you only want a result if the key appears in both dictionaries, in which case I'd do:

dict3 = {key: {**dict1[key], **dict2[key]} 
         for key in dict1.keys() & dict2.keys()}

score 5 · Accepted Answer · answered Jun 06 '18 at 09:11

5

Just use a mix of dict comprehensions and dict unpacking:

dict1 = {'color': {'attri':['Black']}, 'diameter': {'attri':['(300, 600)']}}
dict2 = {'size': {'op':'in'}, 'diameter': {'op':'range'}, 'color': {'op':'in'}}

dict3 = {n:{**dict1[n],**dict2[n]} for n in dict1}

answered Jun 06 '18 at 09:11

MegaIng

7,361
1
22
35

Thanks This is working, How can I also do this if dict1 = {'color': ['Black'], 'diameter': ['(300, 600)']} – Aakash Patel Jun 06 '18 at 09:22
@AakashPatel What should happen then? – MegaIng Jun 06 '18 at 09:27
I am getting the following error :Traceback (most recent call last): File "C:/Users/AAKASH PATEL/Desktop/demo1.py", line 4, in dict3 = {n:{**dict1[n],**dict2[n]} for n in dict1} File "C:/Users/AAKASH PATEL/Desktop/demo1.py", line 4, in dict3 = {n:{**dict1[n],**dict2[n]} for n in dict1} TypeError: 'list' object is not a mapping – Aakash Patel Jun 06 '18 at 09:29
@AakashPatel Yes, because `list` can't be unpacked like that. It doesn't make sense to transform a `list` to a `dict`. What do you expect to happen? – MegaIng Jun 06 '18 at 12:10

score 3 · Answer 3 · answered Jun 06 '18 at 09:14

3

res = {}
for item in dict1:
  res.setdefault(item, {})
  res[item].update(dict1[item])
  if item in dict2:
    res[item].update(dict2[item])

answered Jun 06 '18 at 09:14

ravi

10,994
1
18
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Thanks This is working, How can I also do this if dict1 = {'color': ['Black'], 'diameter': ['(300, 600)']} – Aakash Patel Jun 06 '18 at 09:26

score -1 · Answer 4 · answered Jun 06 '18 at 09:13

-1

For dictionaries x and y, z becomes a merged dictionary with values from y and from x.

In Python 3.5 or greater, :

z = {**x, **y}

In Python 2, (or 3.4 or lower) write a function:

def merge_two_dicts(x, y):
    z = x.copy()   # start with x's keys and values
    z.update(y)    # modifies z with y's keys and values & returns None
    return z
and

z = merge_two_dicts(x, y)

answered Jun 06 '18 at 09:13

Rubin bhandari

1,873
15
20

This isn't what OP wants. Look at the expected result of `dict3`. – FHTMitchell Jun 06 '18 at 09:14

How to combine the dictionaries in python

4 Answers4