Python | Creating Multidimensional dictionary

Sometimes, while working with Python dictionaries we need to have nested dictionaries. But the issue is that, we have to declare before initializing a value in nested dictionary. Let’s resolve this particular problem via methods discussed in this article.

Method #1 : Using setdefault()
This function is used to define an empty dictionary on 1st nested level of dictionary to make it 2D. In this case there is no need to define explicit dictionaries at that level of dictionary. 

Python3

# Python3 code to demonstrate working of
# Creating Multidimensional dictionary
# Using setdefault()

# Initialize dictionary
test_dict = {}

# printing original dictionary
print("The original dictionary : " +  str(test_dict))

# Using setdefault()
# Creating Multidimensional dictionary
test_dict.setdefault(1, {})[4] = 7

# printing result
print("Dictionary after nesting : " + str(test_dict))

Output : 

The original dictionary : {}
Dictionary after nesting : {1: {4: 7}}

Time Complexity: O(n), where n is the length of the list test_dict
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the res list

Method #2 : Using defaultdict()
One can achieve the creation of multi nesting using defaultdict(). Not only at one level, but till N level the nesting can be achieved using this. Drawback is that it creates the defaultdict objects.

Python3

# Python3 code to demonstrate working of
# Creating Multidimensional dictionary
# Using defaultdict()
from collections import defaultdict

# Utility function to create dictionary
def multi_dict(K, type):
    if K == 1:
        return defaultdict(type)
    else:
        return defaultdict(lambda: multi_dict(K-1, type))

# Initialize dictionary
test_dict = {}

# printing original dictionary
print("The original dictionary : " +  str(test_dict))

# Using defaultdict()
# Creating Multidimensional dictionary
# calling function
test_dict = multi_dict(3, int)
test_dict[2][3][4] = 1

# printing result
print("Dictionary after nesting : " + str(dict(test_dict)))

Output : 

The original dictionary : {}
Dictionary after nesting : {2: defaultdict(<function multi_dict.<locals>.<lambda> at 0x7f8707a54158>, {3: defaultdict(<class 'int'>, {4: 1})})}