Python For Loops: The Complete Tutorial with Examples

What is a For Loop?

A for loop repeats a block of code for each item in a sequence. It's Python's primary tool for iteration.

for item in sequence:
    # code that runs for each item

Looping Over a List

students = ["Chan", "Lee", "Wong", "Cheung"]
for name in students:
    print(f"Hello, {name}!")

Looping with range()

range() generates a sequence of numbers:

# 0 to 4 (5 numbers)
for i in range(5):
    print(i)

# 1 to 10
for i in range(1, 11):
    print(i)

# Even numbers 0 to 10
for i in range(0, 11, 2):
    print(i)

# Counting down
for i in range(10, 0, -1):
    print(i)

Looping with Index using enumerate()

students = ["Chan", "Lee", "Wong"]
for i, name in enumerate(students):
    print(f"{i+1}. {name}")

# Output:
# 1. Chan
# 2. Lee
# 3. Wong

Parallel Iteration with zip()

names = ["Chan", "Lee", "Wong"]
scores = [85, 72, 91]

for name, score in zip(names, scores):
    print(f"{name}: {score}")

Looping Over a String

for char in "HKDSE":
    print(char)
# Prints H, K, D, S, E on separate lines

Looping Over a Dictionary

grades = {"Chan": "A", "Lee": "B", "Wong": "A"}

# Keys only
for name in grades:
    print(name)

# Keys and values
for name, grade in grades.items():
    print(f"{name}: {grade}")

Nested Loops

Loops inside loops are essential for 2D data:

# Multiplication table
for i in range(1, 6):
    for j in range(1, 6):
        print(f"{i*j:3}", end=" ")
    print()   # new line after each row

# Output:
#   1   2   3   4   5
#   2   4   6   8  10
#   3   6   9  12  15
#   4   8  12  16  20
#   5  10  15  20  25

Accumulator Pattern

The most common use of loops — building up a value:

scores = [85, 72, 91, 68, 79]

# Sum
total = 0
for score in scores:
    total += score
print(f"Total: {total}")

# Count passes (>=50)
passes = 0
for score in scores:
    if score >= 50:
        passes += 1
print(f"Passes: {passes}")

# Find maximum manually
highest = scores[0]
for score in scores:
    if score > highest:
        highest = score
print(f"Highest: {highest}")

break and continue

# break — exit the loop early
for i in range(10):
    if i == 5:
        break
    print(i)   # 0, 1, 2, 3, 4

# continue — skip this iteration
for i in range(10):
    if i % 2 == 0:
        continue
    print(i)   # 1, 3, 5, 7, 9

Real HK Example: MTR Fare Calculator

fares = [4.5, 6.5, 8.0, 11.5]
total_spent = 0

for trip_num, fare in enumerate(fares, start=1):
    total_spent += fare
    print(f"Trip {trip_num}: ${fare}")

print(f"Total: ${total_spent:.2f}")

When to Use For vs While

• Use for when you know how many times to loop (or have a sequence)
• Use while when you loop until a condition changes