Python – Change Dictionary Items

Welcome to The Coding College, your trusted resource for mastering programming concepts! Today, we’ll explore how to change dictionary items in Python. This skill is essential for managing and updating data dynamically in your programs.

Understanding Dictionary Items

A dictionary in Python stores data as key-value pairs. You can easily update or modify these pairs using specific techniques.

Example of a Dictionary:

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

Here, name, age, and city are keys, while "Alice", 25, and "New York" are their respective values.

Changing Dictionary Items

To modify a dictionary item, simply assign a new value to an existing key.

Syntax:

dictionary[key] = new_value

Example 1: Update a Single Item

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

# Update the value of the 'age' key  
person["age"] = 26  

print(person)

Output:

{'name': 'Alice', 'age': 26, 'city': 'New York'}

Adding a New Key-Value Pair

If the key doesn’t exist in the dictionary, assigning a value to it creates a new key-value pair.

Example 2: Add a New Key

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'}

Updating Multiple Items

You can use the update() method to modify multiple key-value pairs simultaneously.

Syntax:

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

Example 3: Update Multiple Items

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

# Update multiple items  
person.update({"age": 26, "city": "New York"})  

print(person)

Output:

{'name': 'Alice', 'age': 26, 'city': 'New York'}

Modify Nested Dictionary Items

When dictionaries contain other dictionaries as values, you can access and modify the nested items using their keys.

Example 4: Modify a Nested Item

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

# Update the 'age' inside the nested dictionary  
person["details"]["age"] = 26  

print(person)

Output:

{'name': 'Alice', 'details': {'age': 26, 'city': 'New York'}}

Best Practices for Changing Dictionary Items

  • Check if a Key Exists: Use the in keyword to verify a key before updating. 
if "city" in person:  
    person["city"] = "Los Angeles"
  • Use Default Values for Missing Keys: Use the get() method to avoid KeyError. 
person["country"] = person.get("country", "USA")
  • Leverage the update() Method: Update multiple items efficiently without repetitive assignments.

Practice Exercises

Exercise 1: Update an Item

Given the dictionary:

student = {"name": "John", "grade": "B", "age": 20}
  • Change the value of grade to "A".

Exercise 2: Add a New Key-Value Pair

Using the same dictionary, add the key-value pair "city": "London".

Exercise 3: Modify a Nested Dictionary

Given the dictionary:

employee = {"id": 101, "info": {"name": "Sarah", "department": "HR"}}
  • Update the value of department to "IT".

Why Learn with The Coding College?

At The Coding College, we prioritize hands-on learning and user-focused content. Mastering how to change dictionary items is a foundational skill that opens up endless possibilities in programming.

Conclusion

Python dictionaries are dynamic, allowing you to modify key-value pairs with ease. Whether updating single items, adding new pairs, or working with nested dictionaries, Python offers intuitive methods to handle it all.

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