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Topic 1: Lists: Operations and Methods

Python for All: Discover, Learn, and Master Lesson 4: Data Structures – Introduction Topic 1: Lists: Operations and Methods

1. Introduction

A list is a mutable, ordered collection of items in Python. Each item inside a list is referred to as an element. Since lists are mutable, their contents can be modified after creation.

2. Creating Lists

You can create lists using square brackets [] and separating items with commas.

python

fruits = ["apple", "banana", "cherry"]

3. Accessing Elements

Elements can be accessed by their index.

python

print(fruits[0])  # Outputs: apple

4. Basic Operations

Length: Find the number of items in a list.

python

print(len(fruits))  # Outputs: 3

Concatenation: Combine two lists.

python

vegetables = ["carrot", "broccoli"]
food = fruits + vegetables
print(food)  # Outputs: ['apple', 'banana', 'cherry', 'carrot', 'broccoli']

Repetition: Repeat a list.

python

print(fruits * 2)  # Outputs: ['apple', 'banana', 'cherry', 'apple', 'banana', 'cherry']

Membership: Check if an item exists in a list.

python

print("apple" in fruits)  # Outputs: True

5. List Methods

append(): Add an element to the end of the list.

python

fruits.append("grape")
print(fruits)  # Outputs: ['apple', 'banana', 'cherry', 'grape']

extend(): Extend a list with another list or iterable.

python

fruits.extend(["mango", "pineapple"])
print(fruits)  # Outputs: ['apple', 'banana', 'cherry', 'grape', 'mango', 'pineapple']

insert(): Insert an element at a specific position.

python

fruits.insert(1, "orange")  # Insert "orange" at the second position
print(fruits)  # Outputs: ['apple', 'orange', 'banana', 'cherry', 'grape', 'mango', 'pineapple']

remove(): Remove the first occurrence of a specific value.

python

fruits.remove("banana")
print(fruits)  # Outputs: ['apple', 'orange', 'cherry', 'grape', 'mango', 'pineapple']

pop(): Remove an element by index and return it. If no index is provided, it removes the last item.

python

removed_fruit = fruits.pop(0)
print(removed_fruit)  # Outputs: apple
print(fruits)  # Outputs: ['orange', 'cherry', 'grape', 'mango', 'pineapple']

index(): Return the index of the first occurrence of a value.

python

position = fruits.index("cherry")
print(position)  # Outputs: 1

count(): Count the occurrences of a value in the list.

python

num_cherries = fruits.count("cherry")
print(num_cherries)  # Outputs: 1

sort(): Sort the list in-place.

python

fruits.sort()
print(fruits)  # Outputs: ['cherry', 'grape', 'mango', 'orange', 'pineapple']

reverse(): Reverse the list in-place.

python

fruits.reverse()
print(fruits)  # Outputs: ['pineapple', 'orange', 'mango', 'grape', 'cherry']

clear(): Remove all elements from the list.

python

fruits.clear()
print(fruits)  # Outputs: []

6. Conclusion

Lists are one of Python’s most versatile and commonly used data structures. Understanding the operations and methods associated with lists provides a robust foundation for tackling more complex problems and data manipulations in Python.

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