Error handling

Add input validation with try/except.

Error handling: guard the empty list

In this lesson you will guard against the empty list error with try/except. Division on an empty list sum([]) / len([]) raises a division-by-zero error:

empty = []
try:
    result = sum(empty) / len(empty)
except ZeroDivisionError:
    print("boş liste")
else:
    print(result)

The starting code includes the previous solutions. You will add the empty list and the try/except block. Since empty is empty, the except block runs and prints boş liste.

This makes the app more robust.

Exercise Write try/except for the empty list

Write empty = []. Inside a try: block write result = sum(empty) / len(empty). Inside an except ZeroDivisionError: block write print("boş liste"). Inside an else: block write print(result).

Show example solution

grades = [85, 90, 78]
print(grades)
grades.append(95)
print("eklendi:", len(grades))
average = sum(grades) / len(grades)
print("ortalama:", average)
empty = []
try:
    result = sum(empty) / len(empty)
except ZeroDivisionError:
    print("boş liste")
else:
    print(result)

Next step: putting it together

Error handling is ready — the app no longer crashes on an empty list. In the final lesson you will combine everything with functions: you will define and call a hesapla function.

This final layer will make the code reusable and organised. Functions are the fundamental way to break code into parts and make it testable. All the pieces of the project now come together.

Test yourself

Complete the except type

try:
    result = sum(empty) / len(empty)
except ____:
    print("boş liste")

Show answer

try:
    result = sum(empty) / len(empty)
except ZeroDivisionError:
    print("boş liste")

What does sum(empty) / len(empty) do when empty = []?
- Raises ZeroDivisionError
- Returns 1
- Returns None
- Returns 0
Show answer

Raises ZeroDivisionError — len([]) is zero; division by zero raises ZeroDivisionError.
Match error handling

try

Protected code
except

Catches the error
ZeroDivisionError

Division by zero
else

Success block

Next lesson: Putting it together

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