How Can I Efficiently Access and Update Nested Dictionary Items in Python Using a List of Keys?

Accessing Nested Dictionary Items Using a List of Keys

Accessing nested dictionary structures can be a common task in Python programming. Here, we explore a more efficient approach than the provided code for retrieving and modifying data within a complex dictionary using a list of keys.

Using reduce() for Enhanced Traversal

The reduce() function is a powerful tool for transforming a sequence of values by applying a single operation. In this case, we can use it to traverse the dictionary structure, reducing the list of keys into a single value. The operator.getitem method is used as the operation to retrieve the next dictionary level at each iteration.

from functools import reduce  # forward compatibility for Python 3
import operator

def get_from_dict(data_dict, map_list):
    return reduce(operator.getitem, map_list, data_dict)

Updating Data with reduce() and operator.setitem

To update nested dictionary values, we can reuse get_from_dict to retrieve the parent dictionary and use the operator.setitem method to set the value.

def set_in_dict(data_dict, map_list, value):
    get_from_dict(data_dict, map_list[:-1])[map_list[-1]] = value

Example Usage

Let's test our code:

data_dict = {
    "a": {
        "r": 1,
        "s": 2,
        "t": 3
        },
    "b": {
        "u": 1,
        "v": {
            "x": 1,
            "y": 2,
            "z": 3
            },
        "w": 3
        }
    }    

map_list = ["a", "r"]
print(get_from_dict(data_dict, map_list))  # Output: 1

map_list = ["b", "v", "y"]
print(get_from_dict(data_dict, map_list))  # Output: 2

map_list = ["b", "v", "w"]
set_in_dict(data_dict, map_list, 4)
print(data_dict)  # Updated dictionary with "w": 4

This enhanced approach leverages powerful Python functions like reduce() and operator.getitem to efficiently perform nested dictionary operations, making your code cleaner and more efficient.

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