Recursive dictionary merge in Python

dict_merge.py

# Copyright 2016-2022 Paul Durivage
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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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import collections

def dict_merge(dct, merge_dct):
    """ Recursive dict merge. Inspired by :meth:``dict.update()``, instead of
    updating only top-level keys, dict_merge recurses down into dicts nested
    to an arbitrary depth, updating keys. The ``merge_dct`` is merged into
    ``dct``.

    :param dct: dict onto which the merge is executed
    :param merge_dct: dct merged into dct
    :return: None
    """
    for k, v in merge_dct.iteritems():
        if (k in dct and isinstance(dct[k], dict) and isinstance(merge_dct[k], dict)):  #noqa
            dict_merge(dct[k], merge_dct[k])
        else:
            dct[k] = merge_dct[k]

Yes of course. Corrected.

Everything works fine if merge_dict is empty. Your version doesn't return a copy but the base dict itself, so that could lead to bugs.