Mapping over dictionary values in Python

Mapping over dictionary values in Python #

To map over a dictionary's values in Python:

1. Use a dict comprehension to iterate over the dictionary's key-value pairs.
2. On each iteration, pass the value as an argument to the function.
3. The dict comprehension will perform the operation for every key-value pair.

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my_dict = {'a': 1, 'b': 2, 'c': 3}


def example_function(val):
    return val + 100


new_dict = {
    key: example_function(value) for key, value in my_dict.items()
}

print(new_dict)  # 👉️ {'a': 101, 'b': 102, 'c': 103}

Dict comprehensions are very similar to list comprehensions.

In the example, we simply pass the value of the current iteration to the function.

An alternative approach is to use a for loop.

To map over a dictionary's keys:

1. Declare a new variable that stores an empty dictionary.
2. Use a for loop to iterate over the dictionary's items.
3. On each iteration, call the function with the value.
4. Assign the key-value pair to the new dictionary.

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my_dict = {'a': 1, 'b': 2, 'c': 3}


def example_function(val):
    return val + 100


new_dict = {}

for key, value in my_dict.items():
    new_dict[key] = example_function(value)

print(new_dict)  # 👉️ {'a': 101, 'b': 102, 'c': 103}

The dict.items method returns a new view of the dictionary's items ((key, value) pairs).

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my_dict = {'id': 1,  'name': 'Alice'}

print(my_dict.items()) # 👉️ dict_items([('id', 1), ('name', 'Alice')])

This gives us access to the key and the value in the for loop.

On each iteration, we call the function with the value and assign the key-value pair to the new dictionary.

This approach might be a bit easier to read if you aren't used to using dict comprehensions.