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Merging two dictionaries in Python

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Dictionary Operations
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schedule Jul 1, 2022
Last updated
local_offer Python
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There are 2 main ways to merge two dictionaries: using a shallow merge or using the dict.update(~) method.

Shallow merge

To create dictionary z from a shallow merge of dictionaries x and y:

x = {'a': 1, 'b': 2}
y = {'b': 3, 'c': 4}
z = {**x,**y}
print(z)
{'a': 1, 'b': 3, 'c': 4}

Note that using this method dictionaries x and y themselves are not modified.

dict.update method

To update dictionary x with elements from dictionary y:

x = {'a': 1, 'b': 2}
y = {'b': 3, 'c': 4}
x.update(y)
print(x)
{'a': 1, 'b': 3, 'c': 4}

Note that dictionary x itself is updated here with key/value pairs from y. As key 'b' already exists in dictionary x, the corresponding value is simply updated from dictionary y.

To keep dictionary x intact, we should generate a copy of it to use for merging:

x = {'a': 1, 'b': 2}
y = {'b': 3, 'c': 4}
z = x.copy()
z.update(y)
print(z)
{'a': 1, 'b': 3, 'c': 4}
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Published by Isshin Inada
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