Indexing and Slicing in Python Lists Read

Indexing and slicing are fundamental operations to access and extract elements from a list in Python.

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1. Indexing (Accessing Single Elements)

• Lists are zero-indexed (first element is at index 0).
• Negative indices count from the end (-1 = last element).

Example 1: Basic Indexing

python

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

# Positive indexing
print(fruits[0])   # "apple" (1st element)
print(fruits[2])   # "cherry" (3rd element)

# Negative indexing
print(fruits[-1])  # "fig" (last element)
print(fruits[-3])  # "cherry" (3rd from the end)

Output:

text

apple
cherry
fig
cherry

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2. Slicing (Extracting a Sub-List)

• Syntax: list[start:stop:step]
  • start (inclusive), stop (exclusive), step (optional, default=1).
• Omitting start or stop slices from the start/end.

Example 2: Basic Slicing

python

numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# Get elements from index 2 to 5 (exclusive)
print(numbers[2:5])   # [2, 3, 4]

# From start to index 4
print(numbers[:4])    # [0, 1, 2, 3]

# From index 6 to end
print(numbers[6:])    # [6, 7, 8, 9]

# Every 2nd element
print(numbers[::2])   # [0, 2, 4, 6, 8]

# Reverse the list
print(numbers[::-1])  # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

Output:

text

[2, 3, 4]
[0, 1, 2, 3]
[6, 7, 8, 9]
[0, 2, 4, 6, 8]
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]