Create Nested Dictionary using given List - Python
Last Updated :
04 Feb, 2025
The task of creating a nested dictionary in Python involves pairing the elements of a list with the key-value pairs from a dictionary. Each key from the list will map to a dictionary containing a corresponding key-value pair from the original dictionary. For example, given the dictionary a = {'Gfg': 4, 'is': 5, 'best': 9} and the list b = [8, 3, 2], the task is to create a nested dictionary like this:{8: {'Gfg': 4}, 3: {'is': 5}, 2: {'best': 9}} .
Using zip()
zip() pair elements from two or more iterables. In this case, it pairs the elements of the list with the key-value pairs from the dictionary. After pairing the elements, We can create a nested dictionary by iterating over the zipped pairs.
Python
a = {'Gfg': 4, 'is': 5, 'best': 9}
b = [8, 3, 2]
res = {key: {k: v} for key, (k, v) in zip(b, a.items())}
print(res)
Output{8: {'Gfg': 4}, 3: {'is': 5}, 2: {'best': 9}}
Explanation: zip(b, a.items()) pairs each element of b with a key-value pair from a, assigning the list element to key and the dictionary pair to (k, v). The comprehension {key: {k: v}} then creates a nested dictionary where each key from b maps to its corresponding {k: v} from a.
Using for loop
This method also uses the zip() function, but the key difference is that the looping process is slightly more explicit and manual. Here, we directly iterate over the zipped elements without using dictionary comprehension.
Python
a = {'Gfg': 4, 'is': 5, 'best': 9}
b = [8, 3, 2]
res = {}
for key, (k, v) in zip(b, a.items()):
res[key] = {k: v}
print(res)
Output{8: {'Gfg': 4}, 3: {'is': 5}, 2: {'best': 9}}
Explanation: for loop uses zip(b, a.items()) to pair each element from b with a key-value pair from a. For each pair, res[key] = {k: v} assigns a nested dictionary {k: v} to key, creating res where each key from b maps to the corresponding key-value pair from a.
Using dict()
While this method uses zip() to pair the list and dictionary items, it applies the dict() constructor to explicitly create the final nested dictionary. In this case, the dict() constructor is used with a lambda function to wrap each value in another dictionary.
Python
a = {'Gfg': 4, 'is': 5, 'best': 9}
b = [8, 3, 2]
res = dict(map(lambda key_val: (key_val[0], {key_val[1][0]: key_val[1][1]}), zip(b, a.items())))
print(res)
Output{8: {'Gfg': 4}, 3: {'is': 5}, 2: {'best': 9}}
Explanation: zip(b, a.items()) to pair elements from b with key-value pairs from a. The map with lambda creates tuples where each element from b is a key, and its value is a nested dictionary from a. dict() then converts these tuples into the final dictionary res.
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