How to Update a Nested Dictionary While Preserving Specific Key-Value Pairs?

Updating a Nested Dictionary of Varying Depth

To seamlessly update a nested dictionary (dictionary1) with the contents of another nested dictionary (update) while preserving specific key-value pairs, it is necessary to employ a recursive solution that considers the varying depths of the dictionaries.

Consider the following example scenario:

Before Update:

dictionary1 = {
    "level1": {
        "level2": {"levelA": 0, "levelB": 1}
    }
}

update = {
    "level1": {
        "level2": {"levelB": 10}
    }
}

Using the standard update method would overwrite the existing "level2" values in dictionary1, resulting in:

dictionary1.update(update)
print(dictionary1)

{
    "level1": {
        "level2": {"levelB": 10}  # "levelA" is lost
    }
}

Recursive Solution:

To address this preservation requirement, the following Python code provides a recursive solution:

import copy

def update_dictionary(d, u):
    for k, v in u.items():
        if isinstance(v, dict):
            # If the value is a dictionary, recursively update
            d[k] = update_dictionary(d.get(k, {}), v)
        else:
            # If the value is not a dictionary, simply update
            d[k] = copy.deepcopy(v)
    return d

This solution creates a deep copy of the original dictionary1 to prevent in-place updates. It then iterates through the update dictionary (u) and recursively updates the corresponding values in d. If the value is a dictionary, it continues the recursion; otherwise, it updates the value directly.

Usage:

Applying this solution to the earlier example:

result = update_dictionary(dictionary1, update)
print(result)

Result:

{
    "level1": {
        "level2": {"levelA": 0, "levelB": 10}  # "levelA" preserved
    }
}

This solution effectively updates the "levelB" value while preserving the "levelA" value in the original dictionary. It handles nested dictionaries of varying depths, ensuring that specific key-value pairs are preserved during the update process.

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