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I am new to Python and am trying to write a function that will merge two dictionary objects in python. For instance 

dict1 = {'a':[1], 'b':[2]}
dict2 = {'b':[3], 'c':[4]}

I need to produce a new merged dictionary 

dict3 = {'a':[1], 'b':[2,3], 'c':[4]}

Function should also take a parameter “conflict” (set to True or False). When conflict is set to False, above is fine. When conflict is set to True, code will merge the dictionary like this instead: 

dict3 = {'a':[1], 'b_1':[2], 'b_2':[3], 'c':[4]}

I am trying to append the 2 dictionaries, but not sure how to do it the right way.

for key in dict1.keys():
    if dict2.has_key(key):
        dict2[key].append(dict1[key])
Jan Christoph Terasa
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nasia jaffri
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    [`dict2[key].extend(dict1[key])`](http://stackoverflow.com/questions/252703/python-append-vs-extend) – John Kugelman Nov 08 '13 at 15:04
  • Great, thanks extend is doing it the right way, but still I am unable to add 2 dictionaries. With the code that I have, I am only adding onto the keys of dict2 .@ John Kugelman – nasia jaffri Nov 08 '13 at 15:10
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    Huh http://stackoverflow.com/questions/252703/python-append-vs-extend is not an exact duplicate. – kennytm Nov 08 '13 at 15:10
  • Thanks @ Kenny TM. I have a few more questions than that post. I see what is the difference between extend and append, but I want to join the 2 dictionaries. and also if Conflict is set to False, I need to join the keys in a different way. Please guide how to do that. – nasia jaffri Nov 08 '13 at 15:13
  • I hate it when people get on here with there homework questions, which is obviously what nassia is doing. – JPKab Jan 07 '14 at 14:55
  • What did you end up using the accepted answer for? – Noctis Skytower Dec 12 '18 at 21:59
  • The duplicated question is not the answer of this question. This question is the right one. https://stackoverflow.com/questions/10626202/combine-python-dictionaries-that-have-the-same-key-name – Maryam Bahrami Jun 29 '21 at 09:00

2 Answers2

11

If you want a merged copy that does not alter the original dicts and watches for name conflicts, you might want to try this solution:

#! /usr/bin/env python3
import copy
import itertools


def main():
    dict_a = dict(a=[1], b=[2])
    dict_b = dict(b=[3], c=[4])
    complete_merge = merge_dicts(dict_a, dict_b, True)
    print(complete_merge)
    resolved_merge = merge_dicts(dict_a, dict_b, False)
    print(resolved_merge)


def merge_dicts(a, b, complete):
    new_dict = copy.deepcopy(a)
    if complete:
        for key, value in b.items():
            new_dict.setdefault(key, []).extend(value)
    else:
        for key, value in b.items():
            if key in new_dict:
                # rename first key
                counter = itertools.count(1)
                while True:
                    new_key = f'{key}_{next(counter)}'
                    if new_key not in new_dict:
                        new_dict[new_key] = new_dict.pop(key)
                        break
                # create second key
                while True:
                    new_key = f'{key}_{next(counter)}'
                    if new_key not in new_dict:
                        new_dict[new_key] = value
                        break
            else:
                new_dict[key] = value
    return new_dict


if __name__ == '__main__':
    main()

The program displays the following representation for the two merged dictionaries:

{'a': [1], 'b': [2, 3], 'c': [4]}
{'a': [1], 'b_1': [2], 'b_2': [3], 'c': [4]}
Noctis Skytower
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3

I think you want this:

dict1 = {'a':[1], 'b':[2]}
dict2 = {'b':[3], 'c':[4]}

def mergeArray(conflict):
    for key in dict1.keys():
        if dict2.has_key(key):
            if conflict==False:
                dict2[key].extend(dict1[key])
            else:
                dict2[key+'_1'] = dict1[key]
                dict2[key+'_2'] = dict2.pop(key)
        else:
            dict2[key] = dict1[key]

mergeArray(True);
print dict2
Cyrus
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