Chapter 7: Working with Lists and Dictionaries

Discover Python's core data structures, lists and dictionaries, which allow you to store and manage collections of data effectively.

In this chapter, we�ll explore lists and dictionaries in Python. These data structures are fundamental for organizing and managing data collections. By the end, you�ll be able to create, modify, and utilize lists and dictionaries in your programs.

Introduction to Lists

A list is an ordered collection of items that can store multiple values of different data types. Lists are defined using square brackets []:

fruits = ["apple", "banana", "cherry"]
print(fruits)

In this example, fruits is a list containing three items.

Accessing and Modifying Lists

You can access list items by their index and modify them directly:

fruits = ["apple", "banana", "cherry"]
print(fruits[0])   # Output: apple
fruits[1] = "blueberry"
print(fruits)

Here, we changed the second item in the list to "blueberry".

List Methods

Python provides various methods to work with lists. Here are some common ones:

append(): Adds an item to the end of the list.
insert(): Inserts an item at a specific position.
remove(): Removes the first occurrence of an item.
pop(): Removes an item by index.
sort(): Sorts the list in ascending order.

fruits = ["apple", "banana", "cherry"]
fruits.append("orange")
print(fruits)    # Output: ['apple', 'banana', 'cherry', 'orange']

Introduction to Dictionaries

A dictionary is a collection of key-value pairs, where each key is unique. Dictionaries are defined using curly braces {}:

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

In this example, person is a dictionary with three key-value pairs.

Accessing and Modifying Dictionaries

You can access and modify values in a dictionary using keys:

print(person["name"])   # Output: Alice
person["age"] = 30
print(person)

Here, we changed the value of the age key to 30.

Dictionary Methods

Python provides various methods to work with dictionaries. Here are some useful ones:

keys(): Returns a list of all keys in the dictionary.
values(): Returns a list of all values in the dictionary.
items(): Returns a list of key-value pairs.
get(): Retrieves a value for a specified key.
pop(): Removes an item by key.

print(person.keys())    # Output: dict_keys(['name', 'age', 'city'])
print(person.values())  # Output: dict_values(['Alice', 30, 'New York'])

Summary and Next Steps

In this chapter, we covered Python�s list and dictionary data structures, including how to create, modify, and use them. Lists and dictionaries are powerful tools for handling collections of data. In the next chapter, we�ll dive into working with files, where you�ll learn how to read from and write to files in Python.