PythonLesson 13 of 16

Errors and try/except in Python

In Python an error is called an exception: the program stops and tells you what went wrong. try/except lets you catch it and carry on.

Key points

The last line of a traceback names the error and its cause
try: holds risky code; except SomeError: says what to do if it fails
Catch specific errors: ValueError, ZeroDivisionError, KeyError
finally runs no matter what
raise ValueError("...") throws an error yourself when data is wrong

Example

try:    number = int("abc")except ValueError:    print("That is not a number") try:    print(10 / 0)except ZeroDivisionError as error:    print("Oops:", error)finally:    print("Done")

Both errors were caught and the program ran to the end. as error gave access to the message, and finally ran either way.

Task

How to use the editor⌘ Enter or Ctrl Enter runs the code, ⇧ ⌘ Enter checks the task.Tab and Shift Tab indent the line or the selection; Esc, then Tab leaves the editor.The check compares what the program printed with the task; spaces at line ends do not matter.After two failed checks you may open the solution. Your code is kept in this browser.

Survey answers arrived as text, and not all of them are numbers. Add the ones that convert to a number into total and count the rest in skipped.

answers = ["12", "7", "abc", "5", ""]total = 0skipped = 0for value in answers:    # TODO: add int(value) to total; if that fails, count it in skipped    passprint("Total:", total)print("Skipped:", skipped)

answers = ["12", "7", "abc", "5", ""]
total = 0
skipped = 0
for value in answers:
    # TODO: add int(value) to total; if that fails, count it in skipped
    pass
print("Total:", total)
print("Skipped:", skipped)

Output

What your program prints appears here.