Jump from try to except using python

Question

I searching the way to break the try and go into the except (This example has an syntaxerror in the break line)

def fool():
    return 0

try:
    var = fool()
    if var == 0:
        pass  # from here jump to except 
except:
    fool2()

Another way i thought is:

var = fool()
if var == 0:
     fool2()

Another solution more pythonic ?

Answer 1

You can raise a generic Exception:

try:
    var = fool()
    if var == 0:
        raise Exception
except:
    fool2()

But this is not good programming: you should always be clear on which exceptions you're going to catch.

The Zen of Python states that "Errors should never pass silently".

So, this could be a better implementation:

class FoolException(Exception):
    pass

def fool():
    if everything_ok:       
        return 0
    raise FoolException()


try:
    var = fool()
    if var == 0:
        raise FoolException() 
except FoolException:
    fool2()

This will prevent you to catch unwanted exceptions (e.g. IndexError, ZeroDivisionError...)

BUT, I think the best pattern here is to call fool2 separately:

def fool():
    return 0


try:
    var = fool()
    if var == 0: #Here I manage controlled events
        fool2()
except: #Here I manage uncontrolled events
    fool2()

This way is even better, because it isolates the instruction which can raise exceptions:

def fool():
    return 0


try:
    var = fool()
except: #Here I manage uncontrolled events
    fool2()
else:  #Here I manage controlled events
    if var == 0:
        fool2()