Merge two dictionaries and persist the values of first dictionaries

Question

I have two dictionaries:

first = {"phone": {
                "home": "(234) 442-4424"
            },
         "address":"xyz" 
            }


second = {"phone": {
                "home": "(234) 442-4424",
                "home1": "(234) 442-4424"
            },
         "address":{} 
            }

I want merge two dictionaries first over second, meaning the first dictionary doesn't lose its previous values and only the missing key values are added into first.

The final dictionary should look like this:

final = {"phone": {
                "home": "(234) 442-4424",
                "home1": "(234) 442-4424"
            },
         "address":"xyz" 
            }

Also what if when we use list of dictionaries like : -

    first = {"phone": {
                "home": "(234) 442-4424"
            },
         "address":[{"home":""},{"office":""}]
            }

score 4 · Answer 1 · answered Nov 25 '15 at 09:31

4

Do second.update(first). Any keys in both will have their value set to the value in first and any keys that are in first but not second will be added to second.

answered Nov 25 '15 at 09:31

El'endia Starman

2,204
21
35

yes I have used this but I dont want change first key value. – user3048148 Nov 25 '15 at 09:47
@user3048148: If you don't want to change either dictionary, then do `third = second.copy()` and then `third.update(first)`. – El'endia Starman Nov 25 '15 at 20:23

score 1 · Accepted Answer · answered Nov 25 '15 at 12:56

1

Update() will work, simply copy the second dict and apply the first one. So the value of the first will replace the second and not the reverse way.

first = {"phone": {"home": "(234) 442-4424"},"address":"xyz"}
second = {"phone": {"home": "(234) 442-5555","home1": "(234) 442-4424"},"address":{}}

# recursive deep update you can find here: http://stackoverflow.com/a/3233356/956660
import collections

def update(d, u):
    for k, v in u.iteritems():
        if isinstance(v, collections.Mapping):
            r = update(d.get(k, {}), v)
            d[k] = r
        else:
            d[k] = u[k]
    return d

third = second.copy()
update(third, first)

print(third)

{'phone': {'home': '(234) 442-4424', 'home1': '(234) 442-4424'}, 'address': 'xyz'}

answered Nov 25 '15 at 12:56

Cyrbil

6,341
1
24
40

great it is working as required. Let me understand the logic which u have used. – user3048148 Nov 26 '15 at 05:26
Hi cyrbil, It is working fine but fail when we take list of dictionaries in it. I am beginners in python so unable to figure out how to fix this. I have updated the ticket. – user3048148 Dec 17 '15 at 09:03
Hi, please post another question for that. Addressing one issue at a time. – Cyrbil Dec 17 '15 at 10:17

Arnab Datta · Answer 3 · 2015-11-25T09:52:55.397

0

If you want to just add the missing key/value pairs into the first dictionary, you can just add them to the first instead of creating a new dictionary.

first = {}
second = {}

for key in second.keys():
  if key not in first:
    first[key] = second[key]

Edit: your comment "it wont work with multilevel dictionary"

Actually, it will..technically speaking.

first = {"Person1" : {"Age": "26", "Name": "Person1", "Phone number": "XXXXXX"}}
second = {"Person1": {"Interests": "fishing"}, "Person2": {"Age": "26", "Name": "Person2", "Phone number": "XXXXXX"}}

In this case, the firstdict will get the Person2object, but will not change the Person1 object, as it is already there!

edited Nov 25 '15 at 09:52

answered Nov 25 '15 at 09:32

Arnab Datta

5,356
10
41
67

but it wont work with multi level dictionary – user3048148 Nov 25 '15 at 09:41
@user3048148 you didn't specified whether your dict is multilevel or not. – Manish Gupta Nov 25 '15 at 09:46

score 0 · Answer 4 · answered Nov 25 '15 at 10:06

Assuming your dictionnaries have following structure:

each element is a dictionnary
values are either plain strings or dictionnaries

Assuming that the requirement is:

if a key exist only in one of the 2 elements to merge, keep its value
if a key exists in both elements:
- if the value in first element is a plain string, keep its value
- if the value in first element is a dict and the value in second is a string, keep value from first
- if the values in both elements are dict merge them with priority to first

A possible code is then:

for k, v in first.iteritems():
    if isinstance(v, str):
        final[k] = v
    elif k in final:
        if isinstance(final[k], dict):
            final[k].update(first[k])
        else:
            final[k] = first[k]
    else:
        final[k] = first[k]

Merge two dictionaries and persist the values of first dictionaries

4 Answers4

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