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Practice

How to Use Dictionaries?

In this lesson, we'll explore how to add, modify, and delete values in dictionaries, and how to use dictionaries with loops in Python.


Adding, Modifying, Deleting Values in a Dictionary​

How can we add or modify data in a dictionary that stores a list of friends?

Let's learn how to add new items to, modify, and delete items from dictionaries.


Adding an Element​

To add a new element to a dictionary, simply assign a value to a new key in the dictionary.

Adding an Element to a Dictionary
friends_ages = {
    "Alice": 25,
    "Bob": 30,
    "Charlie": 28
}

# Add David's age
friends_ages["David"] = 26

print(friends_ages)

When the above code is executed, a new entry "David": 26 is added to the friends_ages dictionary, resulting in the output:

{"Alice": 25, "Bob": 30, "Charlie": 28, "David": 26}


Modifying an Element​

To modify a specific element in a dictionary, use the key of that element to assign a new value.

For instance, to change Alice's age to 26, you can write the code as follows:

Modifying an Element in a Dictionary
friends_ages = {
    "Alice": 25,
    "Bob": 30,
    "Charlie": 28
}

# Change Alice's age to 26
friends_ages["Alice"] = 26

print(friends_ages)

Executing this code changes "Alice": 25 to "Alice": 26.


Deleting an Element​

To remove an unnecessary item from a dictionary, use the del keyword.

For example, to delete Charlie's information, you can write the code as follows:

Deleting an Element from a Dictionary
friends_ages = {
    "Alice": 25,
    "Bob": 30,
    "Charlie": 28
}

# Delete Charlie's information
del friends_ages["Charlie"]

print(friends_ages)

Now, Charlie's item is deleted, resulting in the output {"Alice": 25, "Bob": 30}.


Using Dictionaries with Loops​

To examine all keys and values in a dictionary at once, you can use a loop.

Suppose we have a dictionary storing friends' names and ages, as shown below.

To print all information in the friends_ages dictionary, use the items() method.

Example of Using Dictionaries with Loops
friends_ages = {
    "Alice": 25,
    "Bob": 30,
    "Charlie": 28
}

# Print all friends' names and ages
for name, age in friends_ages.items():
    # name is the key, age is the value
    print(f"{name} is {age} years old.")

The items() method makes all items in the dictionary iterable.

For example, using the items() method on the friends_ages dictionary returns tuples like ("Alice", 25), ("Bob", 30), ("Charlie", 28).

for name, age unpacks the tuples, assigning keys ("Alice", "Bob", "Charlie") to name and values (25, 30, 28) to age.

Using the loop to print all friends' names and ages yields the following output:

Output
Alice is 25 years old.
Bob is 30 years old.
Charlie is 28 years old.

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