Merge Python Dicts

Merging maps/hash tables is a pretty common operation in programming.

Though Python is my fallback language, only today I learned the new way all cool kids use to combine dictionaries in Python 3.5 or higher.

Say we have two dicts:

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

What we want to end up with is a new dict d with merged values. In case the dicts have the same key, the value of dict b will override a.

>>> d
{'x': 1, 'y': 3, 'z': 4}

The new way, using PEP 448 dictionary unpacking:

>>> c = {**a, **b}
>>> c
{'x': 1, 'y': 3, 'z': 4}

We can also add more key,value pairs:

>>> d = {**a, 'stan': 'lee', **b}
>>> d
{'x': 1, 'y': 3, 'Stan': 'Lee', 'z': 4}

Stan Lee RIP


The Python 2 preferred way we all know and love is:

def merge_two_dicts(a, b):
    c = a.copy()
    return c

d = merge_two_dicts(a, b)
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