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Merge two dictionaries in a single expression in Python

Merging two dictionaries: Here, we are going learn how to merge two dictionaries in a single expression in Python programming language?
Submitted by Sapna Deraje Radhakrishna, on October 22, 2019

Until version less than 3.4, in python, it was quite a task (no single line approach available) to merge two dictionaries in a single expression. For instance, in version less than 3.4 we had to do something similar (as below) to merge two dictionaries.

def merge(dict_1, dict_2):
    z = dict_1.copy()   
    z.update(dict_2)    
    return z
    
if __name__ == "__main__":
    dict_1 = {'x':1, 'y':2}
    dict_2 = {'a':3, 'b':4}
    merged_dict = merge(dict_1, dict_2)
    print(merged_dict)

Output

{'x': 1, 'y': 2, 'a': 3, 'b': 4}

In the above example, (ref merge method), the dict_1 is shallow copied to a different variable called z, and the z is then updated with the values of dict_2, which results in the merging of two dictionaries.

Merge two dictionaries in a single line

With python 3.5+, the below approach is generally followed to merge two (or more) dictionaries.

if __name__ == "__main__":
    dict_1 = {'x':1, 'y':2}
    dict_2 = {'a':3, 'b':4}
    merged_dict = {**dict_1, **dict_2}
    print(merged_dict)

Output

{'x': 1, 'y': 2, 'a': 3, 'b': 4}

The above can be used to merge two or more dictionaries, like below,

if __name__ == "__main__":
    dict_1 = {'x':1, 'y':2}
    dict_2 = {'a':3, 'b':4}
    dict_3 = {'p':5, 'q':6}
    merged_dict = {**dict_1, **dict_2, **dict_3}
    print(merged_dict)

However, since most of the organizations have not yet moved to the latest version of Python, the general approach followed is as mentioned in the initial example.

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