What function could you use to create a complete copy of a nested dictionary (a dictionary that has dictionaries as values)?

Question

I've tried many answers such as "dict" "copy" "deepcopy" but can't seem to find the answer for the copy of nested dictionaries

Answer 1

I believe the answer that you are looking for is a function that is part of the copy module named deepcopy. It copies contents of a collection recursively, so that you end up with a deep copy rather than a shallow copy. I've included a little example script below which compares the difference between a shallow and deep copy of a dictionary that contains a dictionary (or two in this case).

The copy method which is part of the dict object, only creates a shallow copy. Instead, you should import the copy module (or just the deepcopy function from this module) and use that.

import copy

dictTwo = { "a": 1, "b": 2, "c": 3 }

dictThree = { "x": 98, "y": 99, "z": 100 }

dictOne = { "d2": dictTwo, "d3": dictThree }

# Shallow copy

dictCopy = dictOne.copy( )

# Deep Copy

dictDeepCopy = copy.deepcopy( dictOne )

# Problem with Shallow copy

dictOne["d2"]["b"] = 0

print ( "Problem with Shallow Copy..." )

print ( "DictOne: ", dictOne, sep="\n\t" )

print ( "DictCopy: ", dictCopy, sep="\n\t" )

print ( "The Shallow Copy changes as well when the original is modified." )

# Benefit of Deep copy

print ( "\nBenefit of Deep Copy..." )

print ( "DictOne: ", dictOne, sep="\n\t" )

print ( "DictDeepCopy: ", dictDeepCopy, sep="\n\t" )

print ( "The Deep Copy remains unchanged even though the original is modified." )