Get a comprehensive introduction to Python dictionaries in my blog post here.

update()

The simplest way to update an existing dictionary with the contents of another dictionary is to use the update() method.

doses_finance = {'Alice': 0, 'John': 1}

doses_marketing = {'Rick': 2}

doses_finance.update(doses_marketing)

print(doses_finance)
# {'Alice': 0, 'John': 1, 'Rick': 2}

Note that the update() method modifies the existing dictionary in place and returns no value.

bitwise OR

Starting with Python 3.9, we can use the | (bitwise OR) and |= (in-place bitwise OR) operators to perform dictionary merge and update operations.

The resulting dictionary will be a completely new object that will have the keys from the source dictionaries.

doses_finance = {'Alice': 0, 'John': 1}

doses_marketing = {'Rick': 2}

doses_finance_marketing = doses_finance | doses_marketing

print(doses_finance_marketing)
# {'Alice': 0, 'John': 1, 'Rick': 2}

in-place bitwise OR

We can update a dictionary with the keys coming from a different dictionary using the in-place bitwise OR (|=) operator.

doses_finance = {'Alice': 0, 'John': 1}

doses_finance |= {'Rick': 2}

print(doses_finance)
# {'Alice': 0, 'John': 1, 'Rick': 2}