Recently in a Python webinar the topic of discussion was on adding items to the dictionary. I explored more about this topic and In this tutorial, I will explain how to add items to a dictionary in Python along with suitable examples and screenshots.
Add Items to a Dictionary in Python
Let us learn how to add items to a dictionary in Python.
Read How to Sort a Dictionary by Value in Python?
1. Add a Single Key-Value Pair
The simplest way to add a new item to a Python dictionary is by using the square bracket notation. Here’s an example:
person = {"name": "John", "age": 25}
person["city"] = "New York"
print(person)Output:
{'name': 'John', 'age': 25, 'city': 'New York'}You can refer to the screenshot below to see the output.
In this example, we start with a person dictionary containing two key-value pairs. To add a new item, we simply assign a value to a new key using the square bracket notation. Here, we add the key "city" with the value "New York" to the person dictionary. You can add a key-value pair to a dictionary using the assignment operator =.
Check out Python Sort Dictionary By Key
2. Add Multiple Key-Value Pairs
If you need to add multiple key-value pairs to a dictionary at once, you can use the update() method in Python. Here’s an example:
state_capitals = {"California": "Sacramento", "New York": "Albany"}
new_capitals = {"Texas": "Austin", "Florida": "Tallahassee"}
state_capitals.update(new_capitals)
print(state_capitals)Output:
{'California': 'Sacramento', 'New York': 'Albany', 'Texas': 'Austin', 'Florida': 'Tallahassee'}You can refer to the screenshot below to see the output.
In this example, we have two dictionaries: state_capitals and new_capitals. We want to add all the key-value pairs from new_capitals to state_capitals. By calling the update() method on state_capitals and passing new_capitals as an argument, we merge the two dictionaries. The update() method is a convenient way to add multiple key-value pairs to a dictionary in Python.
3. Add Items Conditionally
Sometimes, you may want to add an item to a dictionary only if the key doesn’t already exist. You can achieve this using the Python setdefault() method. Here’s an example:
employee_roles = {"John": "Manager", "Emily": "Developer"}
employee_roles.setdefault("John", "Analyst")
employee_roles.setdefault("Michael", "Analyst")
print(employee_roles)Output:
{'John': 'Manager', 'Emily': 'Developer', 'Michael': 'Analyst'}You can refer to the screenshot below to see the output.
In this example, we have an employee_roles dictionary storing the roles of employees. We want to add the role “Analyst” for “John” and “Michael”, but only if they don’t already have a role assigned. By using setdefault() if the key “John” already exists, its value remains unchanged as “Manager”. However, since “Michael” doesn’t exist in the dictionary, a new key-value pair "Michael": "Analyst" is added. The setdefault() method is useful when you want to conditionally add items to a dictionary.
Read Python Increment Value in Dictionary
4. Add Items Using Loops
When you have a large number of items to add to a Python dictionary, using loops can be more efficient. Here’s an example:
cities = ["New York", "Los Angeles", "Chicago", "Houston"]
population = [8336817, 3898747, 2746388, 2320268]
city_population = {}
for city, pop in zip(cities, population):
city_population[city] = pop
print(city_population)Output:
{'New York': 8336817, 'Los Angeles': 3898747, 'Chicago': 2746388, 'Houston': 2320268}In this example, we have two lists: cities and population, representing the names of cities and their respective populations. We want to create a dictionary city_population where the keys are the city names, and the values are the corresponding populations. By using a for loop and the zip() function, we iterate over the two lists simultaneously and add each city-population pair to the dictionary. Loops provide a concise way to add multiple items to a dictionary based on existing data.
Check out How to Find Duplicate Values in Dictionary Python
Conclusion
In this tutorial, I explained how to add items to a dictionary in Python. We learned how to add a single key-value pair using square bracket notation, add multiple pairs using the update() method, conditionally add items with setdefault(), and efficiently add items using loops.
You can also read:
- How to Find Max Value in Python Dictionary
- How to Find Python Dictionary Index
- How to Check If Two Dictionaries are Equal in Python
Bijay Kumar is an experienced Python and AI professional who enjoys helping developers learn modern technologies through practical tutorials and examples. His expertise includes Python development, Machine Learning, Artificial Intelligence, automation, and data analysis using libraries like Pandas, NumPy, TensorFlow, Matplotlib, SciPy, and Scikit-Learn. At PythonGuides.com, he shares in-depth guides designed for both beginners and experienced developers. More about us.
