Flattening Nested Dictionaries: Compressing Keys

To flatten a nested dictionary, you'll need to recursively iterate through each key and value pair, creating new keys by concatenating the parent key with the current key using a separator, such as an underscore.

Deeper levels of the nested dictionary require further recursion using the same process.

Once you've completed the recursion, create a new dictionary from the flattened items.

Here's an example implementation using Python's collections.abc.MutableMapping:

from collections.abc import MutableMapping

def flatten(dictionary, parent_key='', separator='_'):
    items = []
    for key, value in dictionary.items():
        new_key = parent_key   separator   key if parent_key else key
        if isinstance(value, MutableMapping):
            items.extend(flatten(value, new_key, separator=separator).items())
        else:
            items.append((new_key, value))
    return dict(items)

Example usage:

>>> flatten({'a': 1, 'c': {'a': 2, 'b': {'x': 5, 'y' : 10}}, 'd': [1, 2, 3]})
{'a': 1, 'c_a': 2, 'c_b_x': 5, 'd': [1, 2, 3], 'c_b_y': 10}