12. Dictionaries in Python

Quiz: 0/6

Dictionaries are a way to store and organize related pieces of data in Python. They are useful when you need to quickly look up a value based on a specific key, just like looking up a word in a dictionary to find its meaning.

Each item in a dictionary is a key-value pair, where the key is a unique identifier, and the value is the data associated with that key.

Creating Dictionaries

To create a dictionary, you use curly braces {} and separate each key-value pair with a colon :. Here’s how to create a simple dictionary:

my_dict = {"name": "Alice", "age": 25, "city": "Paris"}

In this example:

• "name", "age", and "city" are the keys.
• "Alice", 25, and "Paris" are the values associated with those keys.

Accessing, adding, updating, and removing key-value pairs

Accessing a value:

To get a value, you use the key inside square brackets []:

print(my_dict["name"])  # Output: Alice

Adding a new key-value pair:

You can add new pairs to the dictionary by assigning a value to a new key:

my_dict["job"] = "Engineer"  # Adds a new key "job" with the value "Engineer"

Updating a value:

You can change the value of an existing key:

my_dict["age"] = 26  # Updates the value of "age" to 26

Removing a key-value pair:

You can remove a pair using the del keyword:

del my_dict["city"]  # Removes the key "city" and its associated value

Iterating over keys, values, and items

You can loop through a dictionary to access its keys, values, or both:

Keys:

for key in my_dict:
    print(key)

This will print each key in the dictionary.

Values:

for value in my_dict.values():
    print(value)

This will print each value in the dictionary.

Key-value pairs:

for key, value in my_dict.items():
    print(f"{key}: {value}")

This will print each key along with its associated value.

Nested Dictionaries

A nested dictionary is a dictionary where the value of a key is another dictionary. This is useful when you want to organize data more hierarchically.

my_dict = {
    "person": {"name": "Bob", "age": 30},
    "city": "New York"
}

In this example, the value for the "person" key is another dictionary containing "name" and "age". You can access data inside nested dictionaries like this:

print(my_dict["person"]["name"])  # Output: Bob

Summary

• Dictionaries are used to store key-value pairs, making it easy to look up data using a key.
• You can create, access, update, and remove key-value pairs.
• You can iterate over the keys, values, or both.
• Nested dictionaries allow you to store more complex, hierarchical data.

Dictionaries are a powerful way to organize and manage data in Python!