Convert Nested Dictionary to List Python

Python dictionaries are versatile data structures that allow the storage of key-value pairs. However, working with nested dictionaries, where values themselves are dictionaries, can sometimes be challenging. In this article, we will explore various simple and commonly used methods to convert a nested dictionary into a list in Python.

Example:

Input: {"a":{"b":"c"}}
Output: ["a","b","c"]

Convert Nested Dictionary to List Python

Below, are the methods to Convert Nested Dictionary to List Python.

• Using Nested Loop
• Using List Comprehension
• Using Recursive Function

Convert Nested Dictionary to List Python Using Nested Loop

In this example, below code initializes a nested dictionary and converts its values into a flat list using a nested loop, with each element representing a key, an inner key, and its corresponding value. The resulting list `l` is printed along with the types of the original dictionary and the generated list.

Python

# Initiating dictionary
dictionary = {"a":{"b":"c"}}

l = []

# converting dictionary values to list
for k,v in dictionary.items():
  for i,j in v.items():
    l.extend([k, i, j])

print(type(dictionary))
print(l)
print(type(l))

Output

<type 'dict'>
['a', 'b', 'c']
<type 'list'>

Convert Nested Dictionary to List Python Using List Comprehension

In this example, below code initializes a nested dictionary and converts its values into a flat list using a list comprehension. Each element in the resulting list `l` represents a key, an inner key, and its corresponding value. The types of the original dictionary and the generated list are then printed.

Python

# Initiating dictionary
dictionary = {"a":{"b":"c"}, "d":{"e":"f"}}

# converting dictionary values to list
l = [p for k,v in dictionary.items() for i,j in v.items() for p in (k, i, j)]

print(type(dictionary))
print(l)
print(type(l))

Output

<type 'dict'>
['a', 'b', 'c', 'd', 'e', 'f']
<type 'list'>

Convert Nested Dictionary to List Python Using Recursive Function

In this example, code defines a `flatten_dict` function that recursively flattens a nested dictionary into a list, preserving the order of keys and values. The `nested_dict` is an example input, and the resulting `flattened_list` contains the flattened elements. The code then prints the types of the original nested dictionary.

Python3

def flatten_dict(d):
    flattened_list = []
    for key, value in d.items():
        flattened_list.append(key)
        if isinstance(value, dict):
            flattened_list.extend(flatten_dict(value))
        else:
            flattened_list.append(value)
    return flattened_list

nested_dict = {"a": {"b": "c"}, "d": {"e": "f"}}
flattened_list = flatten_dict(nested_dict)
print(type(nested_dict))
print(flattened_list)
print(type(flattened_list))

Output

<class 'dict'>
['a', 'b', 'c', 'd', 'e', 'f']
<class 'list'>

Conclusion

Converting a nested dictionary into a list in Python can be accomplished through various methods, each offering its own advantages. Whether you prefer the simplicity of list comprehension, the flexibility of a recursive function, or the functional programming style using itertools.chain, these techniques allow you to handle nested data structures effectively in your Python projects.