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.

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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.