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32. for Loops

1. Introduction​

A for loop is used to iterate over a sequence of items (like a list, string, or range).
It is the most common looping construct in Python when you know the number of iterations in advance.

2. Basic for Loop​

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

for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

3. Iterating Over Strings​

Strings are sequences, so you can loop through characters:

for char in "Python":
    print(char)

4. Using the range() Function​

range() generates a sequence of numbers.

for i in range(5):
    print(i)

Output:

0
1
2
3
4

You can specify start, stop, and step:

for i in range(2, 10, 2):
    print(i)   # 2, 4, 6, 8

5. Looping with Index and Value​

Use enumerate() when you need both index and value.

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

for index, fruit in enumerate(fruits):
    print(index, fruit)

6. Nested for Loops​

for i in range(2):
    for j in range(3):
        print(f"i={i}, j={j}")

7. Using else with for​

The else block runs if the loop finishes normally (not broken).

for i in range(3):
    print(i)
else:
    print("Loop completed")

8. Breaking Out of Loops​

for i in range(10):
    if i == 5:
        break
    print(i)

9. Skipping Iterations with continue​

for i in range(5):
    if i == 2:
        continue
    print(i)

Output:

0
1
3
4

10. Practical Examples​

  • Summing numbers:
total = 0
for i in range(1, 6):
    total += i
print("Sum =", total)
  • Iterating over a dictionary:
person = {"name": "Alice", "age": 25}
for key, value in person.items():
    print(key, "=", value)

11. When to Use for Loops​

  • Iterating over lists, strings, or dictionaries.
  • When you know or can define the range of iterations.
  • For cleaner, more readable code compared to while loops.

12. Next Steps​

✅ You now understand for loops and how to iterate over sequences.
In the next chapter, we’ll explore the range() function in more detail.