Lists

Lists are ordered, mutable collections defined with []. They hold elements of different types.

Methods

• append(), insert(), remove(), pop(), sort()

List Comprehension

[x**2 for x in range(10) if x % 2 == 0]

Syntax

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fruits = ["apple", "banana", "cherry"]
fruits.append("date")
print(fruits[0:2])

squares = [x**2 for x in range(10)]
evens = [x for x in range(20) if x % 2 == 0]

Python Lists

PYTHON

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

print("First:", fruits[0])
print("Last:", fruits[-1])
fruits.append("date")
print("Append:", fruits)

# Slicing
print("Slice:", fruits[1:3])

# Methods
fruits.sort()
print("Sorted:", fruits)
print("Count:", fruits.count("apple"))
print("Index:", fruits.index("banana"))

# Iteration
for fruit in fruits:
    print("Fruit:", fruit)

# List comprehension
squares = [x * x for x in range(1, 6)]
print("Squares:", squares)

Try It Yourself

Practice

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Exercise

Remove duplicates from a list preserving order.

Answer

seen = set()
result = []
for x in [1,2,2,3]:
    if x not in seen:
        seen.add(x)
        result.append(x)

Quick Quiz

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What does [1,2,3][1:3] return?

[1,2]

[2,3]

[1,2,3]

Slicing [1:3] returns elements at index 1 and 2.

Retry Quiz

Interview Questions

When to use tuple vs list?

Tuples for immutable data (dict keys, function returns). Lists for mutable collections.

Next Lesson

Dictionaries