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# Merging two dictionaries in Python

schedule Aug 12, 2023
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There are 2 main ways to merge two dictionaries: using a shallow merge or using the `dict.update(~)` method.

# Shallow merge

To create dictionary `z` from a shallow merge of dictionaries `x` and `y`:

``` x = {'a': 1, 'b': 2}y = {'b': 3, 'c': 4}z = {**x,**y}print(z) {'a': 1, 'b': 3, 'c': 4} ```

Note that using this method dictionaries `x` and `y` themselves are not modified.

# dict.update method

To update dictionary `x` with elements from dictionary `y`:

``` x = {'a': 1, 'b': 2}y = {'b': 3, 'c': 4}x.update(y)print(x) {'a': 1, 'b': 3, 'c': 4} ```

Note that dictionary `x` itself is updated here with key/value pairs from `y`. As key `'b'` already exists in dictionary `x`, the corresponding value is simply updated from dictionary `y`.

To keep dictionary `x` intact, we should generate a copy of it to use for merging:

``` x = {'a': 1, 'b': 2}y = {'b': 3, 'c': 4}z = x.copy()z.update(y)print(z) {'a': 1, 'b': 3, 'c': 4} ```
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