What’s the cleanest way to Python merge dictionaries in a single expression?

General Discussions
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1

I’m looking for a one-liner to Python merge dictionaries x and y into a new dictionary z, where overlapping keys should take the value from y.

Example:

x = {‘a’: 1, ‘b’: 2} y = {‘b’: 3, ‘c’: 4} z = merge(x, y)

Expected result:

{‘a’: 1, ‘b’: 3, ‘c’: 4}

What’s the best single-expression way to achieve this merge behavior in modern Python?

2

I’ve been working with Python for over a decade now, and if you’re using Python 3.9 or later, the cleanest and most intuitive way I’ve seen to python merge dictionaries is with the | operator. It’s tailor-made for this:

z = x | y

This creates a new dictionary z where any overlapping keys will prefer values from y. I like how this doesn’t mutate the original dicts, keeps things tidy, especially in production code.

3

Totally agree, @jacqueline-bosco. For folks who might still be on Python 3.5+ or working across environments, I’ve found unpacking with ** to be super reliable when I need to python merge dictionaries on the fly:

z = {**x, **y}

This also creates a new dict, and like with the merge operator, values from y win if keys clash. I use this a lot in CLI tools and config loaders — keeps the code clean without worrying about version compatibility.

4

Yep, and building on both your points, if you’re dealing with dynamically passed dicts or even custom merging logic, this one’s helped me a lot:

z = dict(x.items() | y.items())

This lets you python merge dictionaries in a way that feels more explicit, especially when visualizing or manipulating key-value pairs during debugging. It gives me more flexibility when chaining transformations or applying filters before merging