List Indexing and Slicing

Precisely accessing and extracting parts of a list — from single items to entire sub-sections using Python's powerful slice notation.

"Indexing gets you one item. Slicing gets you any portion you want. Together, they let you work with exactly the data you need."

— ShurAI

Positive Indexing — Counting from the Start

Every item in a list has a position number starting from 0. Use square brackets to grab any item by its position:

colours = ["red", "green", "blue", "yellow", "purple"]

"red"

-5

"green"

-4

"blue"

-3

"yellow"

-2

"purple"

-1

Cyan row = positive index (0 to 4) · Grey row = negative index (-5 to -1)

python

colours = ["red", "green", "blue", "yellow", "purple"]

print(colours[0])    # red    — first
print(colours[2])    # blue   — third
print(colours[4])    # purple — fifth (last)
print(colours[-1])   # purple — last (negative)
print(colours[-2])   # yellow — second from last

Slicing — Grab a Section

Slicing uses [start:stop] — start is included, stop is not included. Think of it as cutting out a portion of the list:

python

days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]

print(days[0:3])    # ['Mon', 'Tue', 'Wed'] — index 0,1,2
print(days[5:])     # ['Sat', 'Sun']        — index 5 to end
print(days[:5])     # ['Mon','Tue','Wed','Thu','Fri'] — start to 4
print(days[1:4])    # ['Tue', 'Wed', 'Thu']
print(days[-2:])    # ['Sat', 'Sun']        — last 2
print(days[:])      # full copy of the list

days[1:4] → picks index 1, 2, 3 (not 4)

Mon

Tue

1 ←start

Wed

Thu

Fri

4 (stop)

Sat

Sun

Result: ['Tue', 'Wed', 'Thu'] — stop index 4 is NOT included

Step Slicing — Every Nth Item

python

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

# [start:stop:step]
print(nums[0:10:2])   # [0, 2, 4, 6, 8] — every 2nd
print(nums[::3])       # [0, 3, 6, 9]    — every 3rd
print(nums[::-1])      # [9, 8, 7, ... 0] — reversed!
print(nums[8:2:-1])    # [8, 7, 6, 5, 4, 3] — backwards slice

Modifying with Slices

You can replace a whole section of a list in one go:

python

letters = ["a", "b", "c", "d", "e"]

# Replace a slice with new values
letters[1:3] = ["X", "Y", "Z"]
print(letters)    # ['a', 'X', 'Y', 'Z', 'd', 'e']

# Delete a slice
del letters[1:4]
print(letters)    # ['a', 'd', 'e']

Real Example — Top 3 and Bottom 3 Students

python

students = [
    ("Kavya",  95),
    ("Riya",   88),
    ("Arjun",  82),
    ("Sneha",  76),
    ("Dev",    71),
    ("Priya",  65),
    ("Vikram", 58),
]

# Sort by score descending
ranked = sorted(students, key=lambda x: x[1], reverse=True)

# Slice to get top 3 and bottom 3
top3    = ranked[:3]
bottom3 = ranked[-3:]

print("🏆 Top 3:")
for i, (name, score) in enumerate(top3, 1):
    print(f"  {i}. {name} — {score}")

print("\n📚 Need extra help:")
for name, score in bottom3:
    print(f"  {name} — {score}")

output

🏆 Top 3:
  1. Kavya — 95
  2. Riya — 88
  3. Arjun — 82

📚 Need extra help:
  Dev — 71
  Priya — 65
  Vikram — 58

"Slicing is your scalpel. Instead of grabbing the whole list and filtering, you cut out exactly what you need in one clean line."

— ShurAI

🧠 Quiz — Question 1

Given items = [10, 20, 30, 40, 50], what does items[1:4] return?

🧠 Quiz — Question 2

Given x = [1, 2, 3, 4, 5], what does x[-2:] return?

🧠 Quiz — Question 3

What does [1,2,3,4,5,6][::-1] return?

🧠 Quiz — Question 4

Given n = [0,1,2,3,4,5,6,7,8,9], what does n[::2] return?