Add a Key-Value Pair to a Nested Dictionary in Python

Dictionaries in Python are versatile data structures that allow you to store and manipulate key-value pairs. When dealing with nested dictionaries, adding a key-value pair becomes a bit more intricate. In this article, we will explore four simple methods to add a key-value pair to a nested dictionary in Python. To illustrate these methods, we will use a student data dictionary.

Add a Key-Value Pair to a Nested Dictionary in Python

Below, are the ways to Add a Key-Value Pair to a Nested Dictionary in Python.

• Using Square Bracket
• Using update() Method
• Using setdefault() Method

Add Key-Value Pair to Nested Dictionary Using Square Bracket

In this example, below code initializes a nested student data dictionary with information about the name, age, and grades. It then prints the original dictionary. The subsequent line adds a new key-value pair (‘science’: 95) to the ‘grades’ dictionary using square bracket notation.

Python3

# Original Student Data Dictionary
student_data = {
    'name': 'John Doe',
    'age': 20,
    'grades': {
        'math': 90,
        'english': 85,
        'history': 78
    }
}

print("Original Dictionary\n", student_data)

# Using Square Bracket Notation
student_data['grades']['science'] = 95
print("Using Square Bracket Notation\n", student_data)

Output

Original Dictionary
 {'name': 'John Doe', 'age': 20, 'grades': {'math': 90, 'english': 85, 'history': 78}}
Using Square Bracket Notation
 {'name': 'John Doe', 'age': 20, 'grades': {'math': 90, 'english': 85, 'history': 78, 'science': 95}}

Add Key-Value Pair to Nested Dictionary Using update() Method

In this example, below code starts with an original student data dictionary containing information about name, age, and grades. It then prints the original dictionary. The subsequent lines demonstrate updating the ‘grades’ dictionary using the `update()` method, adding new subjects (‘physics’: 88, ‘chemistry’: 92).

Python3

# Original Student Data Dictionary
student_data = {
    'name': 'John Doe',
    'age': 20,
    'grades': {
        'math': 90,
        'english': 85,
        'history': 78
    }
}

print("Original Dictionary\n", student_data)

# Using the `update()` Method
new_subjects = {'physics': 88, 'chemistry': 92}
student_data['grades'].update(new_subjects)
print("Using the `update()` Method\n", student_data)

Output

Original Dictionary
 {'name': 'John Doe', 'age': 20, 'grades': {'math': 90, 'english': 85, 'history': 78}}
Using the `update()` Method
 {'name': 'John Doe', 'age': 20, 'grades': {'math': 90, 'english': 85, 'history': 78, 'physics': 88, 'chemistry': 92}}

Add Key-Value Pair to Nested Dictionary Using setdefault()

In this example, below code begins with an original student data dictionary containing details like name, age, and grades. After printing the original dictionary, it utilizes the `setdefault()` method to add a new subject (‘biology’: 89) to the ‘grades’ dictionary, ensuring the key exists or creating it if absent.

Python3

# Original Student Data Dictionary
student_data = {
    'name': 'John Doe',
    'age': 20,
    'grades': {
        'math': 90,
        'english': 85,
        'history': 78
    }
}

print("Original Dictionary\n", student_data)

# Using the `setdefault()` Method
student_data.setdefault('grades', {})['biology'] = 89
print("Using the `setdefault()` Method\n", student_data)

Output

Original Dictionary
 {'name': 'John Doe', 'age': 20, 'grades': {'math': 90, 'english': 85, 'history': 78}}
Using the `setdefault()` Method
 {'name': 'John Doe', 'age': 20, 'grades': {'math': 90, 'english': 85, 'history': 78, 'biology': 89}}

Conclusion

In conclusion, adding a key-value pair to a nested dictionary in Python involves accessing the nested dictionary at the desired level and assigning the new key-value pair. Utilizing the appropriate syntax for dictionary manipulation ensures seamless integration of data into complex nested structures. This straightforward process empowers developers to efficiently expand and modify nested dictionaries, enhancing flexibility and functionality in their Python programs.