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Python | List value merge in dictionary

  • Last Updated : 11 Jul, 2019

Sometimes, while working with dictionaries, we can have a problem in which we have many dictionaries and we are required to merge like keys. This problem seems common, but complex is if the values of keys are list and we need to add elements to list of like keys. Let’s discuss way in which this problem can be solved.

Method : Using list comprehension + items()
This problem can be solved using list comprehension that can be used to merge the list content and also the items method which can be employed to get the dictionary keys and values.

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# Python3 code to demonstrate working of
# List value merge in dictionary
# Using items() + list comprehension
  
# initializing dictionaries
test_dict1 = {'Gfg' : [1, 2, 3], 'for' : [2, 4], 'CS' : [7, 8]}
test_dict2 = {'Gfg' : [10, 11], 'for' : [5], 'CS' : [0, 18]}
  
# printing original dictionaries
print("The original dictionary 1 is : " + str(test_dict1))
print("The original dictionary 2 is : " + str(test_dict2))
  
# Using items() + list comprehension
# List value merge in dictionary
res = {key: value + test_dict2[key] for key, value in test_dict1.items()}
  
# printing result 
print("The merged dictionary is : " + str(res))
Output :

The original dictionary 1 is : {‘for’: [2, 4], ‘CS’: [7, 8], ‘Gfg’: [1, 2, 3]}
The original dictionary 2 is : {‘for’: [5], ‘CS’: [0, 18], ‘Gfg’: [10, 11]}
The merged dictionary is : {‘for’: [2, 4, 5], ‘CS’: [7, 8, 0, 18], ‘Gfg’: [1, 2, 3, 10, 11]}

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