Errors, files and libraries · Lesson 17 of 25

Handling exceptions

try, except, else and finally without hiding errors.

8 minutes2 games

An exception interrupts normal execution. Put the operation that may fail in try and catch the expected type with except. else runs when try succeeds; finally handles cleanup whether an error occurred or not.

Python

raw = "twelve"
try:
    age = int(raw)
except ValueError:
    print("Enter a whole number")
else:
    print(age + 1)
finally:
    print("Done")

Try conversion

Success → else

ValueError → except

Cleanup → finally

Spot the bug

Which line raises ValueError?

Exercise

Print Invalid if conversion fails.

Expected output: Invalid

Python

raw = "oops"

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Python

Errors, files and libraries · Lesson 17 of 25

Handling exceptions

try, except, else and finally without hiding errors.

8 minutes2 games

Python

raw = "twelve"
try:
    age = int(raw)
except ValueError:
    print("Enter a whole number")
else:
    print(age + 1)
finally:
    print("Done")

Try conversion

Success → else

ValueError → except

Cleanup → finally

Spot the bug

Which line raises ValueError?

Exercise

Print Invalid if conversion fails.

Expected output: Invalid

Python

raw = "oops"

Learn more from

Played 0 of 2 games