Swapping two nested dicts

Question

I am trying to swap nodes between two binary trees, which are represented as nested dicts. I have tried to accomplish this by using a function that takes in a dict and list of keys, performs a deep get on it, and returns the nested dict. e.g.

def deep_get(dictionary, keys, default=None):
    """ By Yuda Prawira
    Source: https://stackoverflow.com/questions/25833613/python-safe-method-to-get-value-of-nested-dictionary"""
    return reduce(lambda d, key: d.get(key, default) if isinstance(d, dict) else default, keys.split("."), dictionary)

However whenever I assign it to a variable and try to do a basic swap, the original dict is unchanged:

a = deep_get(tree1, "left.right.left")
b = deep_get(tree2, "left.right")
c = a.copy()
a.clear()
a.update(b)
b.clear()
b.update(c)

Is there a simpler way of accomplishing this, or will I have to create a tree class that wraps around the dict?

sample input:

tree1 = {'left': {'left': 5, 'op': 'sin', 'right': 1}, 'op': 'cos', 'right': {'op': 'sin', 'right': 3}}
tree2 = {'left': {'left': 1, 'op': 'sin', 'right': 2}, 'op': 'tan', 'right': {'left': 1, 'op': 'sin', 'right': 4}}

First, I choose randomly a node from tree1 and tree2 to swap. Suppose I want to swap the first level left branch of tree1 with the second level right branch of tree2. Then the trees after swap should be like:

tree1 = {'left': {'left': 1, 'op': 'sin', 'right': 4}, 'op': 'cos', 'right': {'op': 'sin', 'right': 3}}
tree2 = {'left': {'left': 1, 'op': 'sin', 'right': 2}, 'op': 'tan', 'right': {'left': 5, 'op': 'sin', 'right': 1}}

I'm not sure I follow what you are doing here, but if these are nested dictionaries do you not need to use [`deepcopy`](https://docs.python.org/2/library/copy.html) rather than `.copy()`? This would be a lot clearer if you provided sample inputs, outputs and expected output. — Dan, Oct 17 '19 at 00:09

Swapping two nested dicts

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