Handling Exceptions with try, except and finally

Handling Exceptions with try, except and finally

An exception is an error raised while the program runs. If nothing handles it, the program stops with a traceback. To handle it, put the risky statements in a try block and the recovery in an except block.

try:
    a = int(input())
    b = int(input())
    result = a / b
except ZeroDivisionError:
    print("Denominator cannot be zero")
except ValueError:
    print("Please enter whole numbers")
else:
    print("Result:", result)   # only when no exception occurred
finally:
    print("Done")               # always runs

• Python tries each except clause in order and runs the first one that matches the exception's type.
• The else block runs only if the try block raised nothing.
• The finally block runs in every case, exception or not. It is the place to close a file or release a resource.
• A bare except: catches everything. Use it sparingly, because it also hides mistakes you would want to see.

total = 0
invalid = 0
while True:
    line = input()
    if line == "END":
        break
    total += int(line)  # wrap this in try / except ValueError
print("Sum:", total)
print("Invalid:", invalid)