Python Dictionary Add Key-Value Pairs: Complete Guide

Examples: Dictionary Add Key-Value

Here are practical examples of adding key-value pairs in a Python dictionary.

Example 1: Add a New Key-Value Pair

A new key is added because it doesn’t already exist in the dictionary

# Create a simple dictionary
student = {"name": "John", "age": 21}

# Add a new key-value pair
student["grade"] = "A"

print(student)


#Output:
{'name': 'John', 'age': 21, 'grade': 'A'}

Explanation: A new key is added to the dictionary. The existing values are not affected. This is one of the most common ways to add data to a dictionary in Python.

Example 2: Update Existing Key’s Value

The existing key is updated with a new value.

# Update an existing value
student = {"name": "John", "age": 21}
student["age"] = 22

print(student)


#Output:
{'name': 'John', 'age': 22}

Explanation: The key age already exists, so its value is updated from 21 to 22. Python simply replaces the old value with the new one. No error is raised during this process.

Example 3: Add Integer Key

Integer keys can also be used in dictionaries.

# Dictionary with integer keys
inventory = {1: "apple", 2: "banana"}

# Add new item
inventory[3] = "cherry"

print(inventory)


#Output: 
{1: 'apple', 2: 'banana', 3: 'cherry'}

Explanation: Integer keys are also allowed in dictionaries. A new numeric key is added with a value. This shows that keys are not limited to strings.

Example 4: Add Key with List as Value

A list is stored as a value under one key.

# Add key with list as value
employee = {"name": "Alice"}
employee["skills"] = ["Python", "Excel"]

print(employee)


#Output:
{'name': 'Alice', 'skills': ['Python', 'Excel']}

Explanation: Here, a list containing multiple skills is stored under the key “skills”. This helps group multiple related items together. It is useful for structured data storage.

Example 5: Add Elements in a Loop

Keys and values are added dynamically inside a loop.

# Create empty dictionary
data = {}

# Add elements using a loop
for i in range(3):
    data[f"item_{i}"] = i * 10

print(data)


#Output:
{'item_0': 0, 'item_1': 10, 'item_2': 20}

Explanation: Keys and values are added repeatedly inside a loop. This reduces manual work. It is useful when handling large or repetitive data.

Example 6: Check Before Adding Using .get()

A key is added only if it doesn’t already exist.

# Create dictionary
profile = {"username": "coder123"}

# Only add 'email' if not present
if profile.get("email") is None:
    profile["email"] = "coder@example.com"

print(profile)


#Output:
{'username': 'coder123', 'email': 'coder@example.com'}

Explanation: Before adding the key email, the code checks whether it already exists using get(). This prevents overwriting existing data and ensures safe insertion. The key is added only when it does not already exist.

Example 7: Add Nested Dictionary

A dictionary is stored inside another dictionary.

# Create empty dictionary
user_data = {}

# Add nested dictionary
user_data["user1"] = {"email": "user1@example.com", "age": 25}

print(user_data)


#Output:
{'user1': {'email': 'user1@example.com', 'age': 25}}

Explanation: A dictionary is stored inside another dictionary to organize related data in a structured way. This approach is commonly used for user profiles, JSON data, and complex application records.

Example 8: Dynamically Add Based on Input

Values are assigned dynamically from a list of pairs.

# Initialize dictionary
results = {}

# Simulate input-driven addition
entries = [("Math", 85), ("Science", 90), ("English", 88)]

for subject, score in entries:
    results[subject] = score

print(results)


#Output:
{'Math': 85, 'Science': 90, 'English': 88}

Explanation: Key-value pairs are added dynamically from a list of tuples, making it easier to create dictionaries from structured or bulk data.