How Can I Efficiently Access and Modify Data in Nested Python Dictionaries Using a List of Keys?

Navigating Nested Dictionaries with a List of Keys

Problem:

How can we efficiently access and manipulate data within a deeply nested dictionary structure using a list of keys?

Solution:

The native Python function functools.reduce can be utilized to traverse the dictionary efficiently in a single pass.

Implementation:

from functools import reduce
import operator

def get_by_path(root, items):
    """Access a nested object in root by item sequence."""
    return reduce(operator.getitem, items, root)

Usage:

To retrieve the value at the specified path, use get_by_path:

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

maplist = ["a", "r"]
value = get_by_path(dataDict, maplist)  # 1

Setting Values:

To set a value at a particular path, we can reuse get_by_path to locate the parent dictionary and assign the value to the desired key:

def set_by_path(root, items, value):
    """Set a value in a nested object in root by item sequence."""
    get_by_path(root, items[:-1])[items[-1]] = value

Usage:

maplist = ["b", "v", "w"]
set_by_path(dataDict, maplist, 4)

Additional Functionality:

For completeness, we can also define a function to delete a key-value pair within the nested dictionary:

def del_by_path(root, items):
    """Delete a key-value in a nested object in root by item sequence."""
    del get_by_path(root, items[:-1])[items[-1]]

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