Errors and Debugging

Errors and Debugging

A program can go wrong in three ways:

• Syntax errors break the rules of the language: a missing colon, an unclosed bracket, wrong indentation. Python refuses to run the program at all and points at the line.
• Runtime errors (exceptions) happen while the program is running: dividing by zero (ZeroDivisionError), converting "abc" with int() (ValueError), using an undefined name (NameError), adding a number to a string (TypeError). The program stops at that line.
• Logical errors give a wrong answer without any message, such as avg = a + b / 2 instead of (a + b) / 2. Only testing with known answers finds them.

Debugging means finding and fixing these errors: read the error message (its last line names the error and the line number), print intermediate values, and test with inputs whose answer you already know.

A preview of Class 12: a runtime error can be handled so the program does not crash.

try:
    print(10 / int(input()))
except ZeroDivisionError:
    print("Cannot divide by zero")

a, b = map(int, input().split())
avg = a + b / 2
print(f"{avg:.1f}")