How to convert a MultiDict to nested dictionary using Python

Last Updated : 24 Apr, 2025

A MultiDict is a dictionary-like object that holds multiple values for the same key, making it a useful data structure for processing forms and query strings. It is a subclass of the Python built-in dictionary and behaves similarly. In some use cases, we may need to convert a MultiDict to a nested dictionary, where each key corresponds to a dictionary of values. In this article, we will discuss the steps required to convert a MultiDict to a nested dictionary in Python.

First of all, install multidict library by writing the following command in your command line or terminal:

pip install multidict

Steps to convert a MultiDict to a nested dictionary:

Import multidict library
Create a MultiDict using the MultiDict() constructor
Iterate over the items in the MultiDict
For each item, check if the key already exists in the nested dictionary.
If the key exists, append the value to the list of values associated with the key.
If the key does not exist, create a new entry in the nested dictionary with the key and a list of values containing the value from the MultiDict.

Example 1:

In the following example, we convert a MultiDict to a nested dictionary.

Python3

# import multidict from multidict import MultiDict  # create a MultiDict data = MultiDict([('key1', 'value1'), ('key2', 'value2'),                   ('key1', 'value3')])  # initialize a nested dictionary nested_dict = {}  # iterate over the items in the MultiDict for key, value in data.items():     # check if the key exists in the nested dictionary     if key in nested_dict:         # append the value to the list of values         # associated with the key         nested_dict[key].append(value)     else:         # create a new entry in the nested dictionary         # with the key and a list of values         nested_dict[key] = [value]  # output the nested dictionary print(nested_dict)

Output:

In this example, Create a MultiDict with keys 'key1' and 'key2' and multiple values. Iterate over the items, add value to the existing key's list or create a new entry with key and value in the nested dictionary. Output is a nested dictionary with keys and lists of values associated with each.

Example 2:

In the following example, we convert a MultiDict to a nested dictionary.

Python3

# import multidict from multidict import MultiDict  # create a MultiDict data = MultiDict([('fruit', 'apple'), ('color', 'red'),                   ('fruit', 'banana'), ('color', 'yellow')])  # initialize a nested dictionary nested_dict = {}  # iterate over the items in the MultiDict for key, value in data.items():     # check if the key exists in the nested dictionary     if key in nested_dict:         # append the value to the list of values         # associated with the key         nested_dict[key].append(value)     else:         # create a new entry in the nested dictionary         # with the key and a list of values         nested_dict[key] = [value]  # output the nested dictionary print(nested_dict)

Output:

In this example, create a MultiDict with two keys 'fruit' and 'color' with multiple values. Iterate over the items, if the key exists, append its value to the list, else create a new entry in the nested dictionary with the key and list of values. The final output is a nested dictionary with keys and lists of values associated with each key.