Python – Add Dictionary Items

Welcome to The Coding College, where programming becomes simple and practical! In this tutorial, we’ll cover how to add items to a dictionary in Python. Dictionaries are one of Python’s most powerful data structures, and learning to modify them is essential for efficient programming.

Adding Items to a Python Dictionary

In Python, dictionaries are mutable, meaning you can add new key-value pairs at any time. If the key already exists, the value associated with it will be updated; otherwise, a new key-value pair is added.

Adding a Single Key-Value Pair

To add a single key-value pair, use the assignment operator = with the desired key and value.

Syntax:

dictionary[key] = value

Example 1: Add a New Key-Value Pair

person = {"name": "Alice", "age": 25}  

# Add a new key-value pair  
person["city"] = "New York"  

print(person)

Output:

{'name': 'Alice', 'age': 25, 'city': 'New York'}

Adding Multiple Items

To add multiple items at once, use the update() method.

Syntax:

dictionary.update({key1: value1, key2: value2, ...})

Example 2: Add Multiple Key-Value Pairs

person = {"name": "Alice", "age": 25}  

# Add multiple key-value pairs  
person.update({"city": "New York", "country": "USA"})  

print(person)

Output:

{'name': 'Alice', 'age': 25, 'city': 'New York', 'country': 'USA'}

Using Dynamic Values to Add Items

You can calculate or generate values dynamically while adding them to a dictionary.

Example 3: Add an Item with a Computed Value

inventory = {"apples": 10, "bananas": 20}  

# Add a new item with a computed value  
inventory["oranges"] = inventory["apples"] + inventory["bananas"]  

print(inventory)

Output:

{'apples': 10, 'bananas': 20, 'oranges': 30}

Adding Items to a Nested Dictionary

If a dictionary contains another dictionary as a value, you can add new key-value pairs to the nested dictionary.

Example 4: Add an Item to a Nested Dictionary

person = {  
    "name": "Alice",  
    "details": {  
        "age": 25,  
        "city": "New York"  
    }  
}  

# Add a new key-value pair to the nested dictionary  
person["details"]["country"] = "USA"  

print(person)

Output:

{'name': 'Alice', 'details': {'age': 25, 'city': 'New York', 'country': 'USA'}}

Best Practices for Adding Items

  • Avoid Duplicate Keys: Ensure your keys are unique; otherwise, existing keys will be overwritten.
  • Use Conditional Checks: If needed, check if a key exists before adding a new key-value pair. 
if "email" not in person:  
    person["email"] = "[email protected]"
  • Update in Bulk: Use the update() method when adding multiple items for cleaner code.

Practice Exercises

Exercise 1: Add a Key-Value Pair

Given the dictionary:

student = {"name": "John", "grade": "A"}
  • Add the key-value pair "age": 20.

Exercise 2: Add Multiple Items

Using the same dictionary, add the key-value pairs "city": "London" and "subject": "Math".

Exercise 3: Add to a Nested Dictionary

Given the dictionary:

employee = {"id": 101, "info": {"name": "Sarah", "department": "HR"}}
  • Add the key-value pair "location": "New York" to the nested dictionary.

Why Learn with The Coding College?

At The Coding College, we provide easy-to-understand tutorials designed to help you learn programming step by step. Adding dictionary items is a fundamental skill that you’ll frequently use when working with Python.

Conclusion

Adding items to a Python dictionary is a simple but powerful operation that enables you to dynamically modify your data structures. Whether you’re adding a single key-value pair, multiple items, or updating nested dictionaries, Python provides straightforward and flexible tools for the job.

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