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.
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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 =.
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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.
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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.
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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
I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.
