Else statement in python

Question

I'm a python beginner. Two quick questions on the code below:

Why can't I ever execute the print("printed valueError")?
Why does the else statement with print("no error occurred") will print no matters what I put in?

The code:

def int_checker(a,b):
try:
    if isinstance(a,int) and isinstance(b,int):
        print('both integers')
    else:
        raise ValueError
        print('printed ValueError')
except:
    print('error occurred')
else:
    print('no error occurred')
finally:
    print('no error occurred')

print(int_checker(1,2))
print(int_checker(1,'a')

`print('printedValueError')` is right after a `raise` statement. When the exception is raised, execution goes to the except block, not to the next line. So that line is unreachable. — khelwood, May 21 '18 at 11:10
As it is now, it is `finally` statement where `no error occured` is printed. — bereal, May 21 '18 at 11:10
And `print('no error occurred')` is in a `finally` block. The point of a `finally` block is that it should *always* be executed regardless of what happens in your `try` block. — khelwood, May 21 '18 at 11:11
Possible duplicate of [How to use "raise" keyword in Python](https://stackoverflow.com/questions/13957829/how-to-use-raise-keyword-in-python) — khelwood, May 21 '18 at 11:12
Thanks a lot! Quick question -- when does the 2nd else statement get executed? Seems like it gets executed only when both inputs are integers. If one of the input is not an integer, we execute the except statement, and then jumps to finally else: print('no error occurred') — D.S, May 21 '18 at 11:16

Tatranskymedved · Answer 1 · 2018-05-21T11:21:53.853

Why can't I ever execute the print("printed valueError")?

It is simply because the code execution will raise ValueError exception and that jumps directly to the except part. To resolve, You can switch lines:

else:
    print('printed ValueError')
    raise ValueError

Why does the else statement with print("no error occurred") will print no matters what I put in?

You are using syntax with try, catch, else, finally. The order of those is:

Run code in try block.
Did some error occured?
- True: execute code in catch block
- False: execute code in else block
Run code in finally block. (This will happen always!)

From the above, the code form finally statement will be run everytime no matter if there was or wasn't error during execution. In most cases it is used e.g. when You open file in try block, read from it and suddenly an error occurs. In that case You want to close the file and clear the references. That code will go to the finally block.

Similar question on SO: Purpose of else and finally in exception handling

Thanks a lot! Quick question -- when does the 2nd else statement get executed? Seems like it gets executed only when both inputs are integers. If one of the input is not an integer, we execute the except statement, and then jumps to finally else: print('no error occurred') — D.S, May 21 '18 at 11:14

score 0 · Answer 2 · answered May 21 '18 at 11:17

Anything in the "finally" block will print every time.

Try this: remove the 'else' from "try" block and add the following to the 'except' block:

print('printed ValueError')
raise ValueError

The 'else' after 'except' will only run if no errors occur

Else statement in python

2 Answers2