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How to merge two Dictionaries in Python

This article shows different ways to merge two Dictionaries in Python.


This article shows different ways to merge two Dictionaries in Python.

Python Dictionaries have an .update(other) function that updates the dictionary with the key/value pairs from other, overwriting existing keys.

This, however, modifies the original dictionary in-place instead of returning a new one.

x = {'a': 1, 'b': 2}
y = {'b': 8, 'c': 9}

x.update(y)
# x: {'a': 1, 'b': 8, 'c': 9}

To create a new dictionary with the merged key/value pairs you can use different methods, depending on which Python version is used.

In Python 3.9 or greater:

z = x | y
# z: {'a': 1, 'b': 8, 'c': 9}

In Python 3.5 or greater:

z = {**x, **y}
# z: {'a': 1, 'b': 8, 'c': 9}

This is also known as dictionary unpacking. It was introduced in
PEP 448.

You can learn more about unpacking and different asterisk (*) use cases here.

Python 3.4 or lower:

z = x.copy()
z.update(y) 

# z: {'a': 1, 'b': 8, 'c': 9}

Note that if you just use z = x, only a shallow copy is created. This means that even after z has been updated, modifying x will also update z, and vice-versa.

So in order to create a true copy, x.copy() is used here. You can learn more about shallow vs. deep copying here.


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