Why isn't my user defined exception being handled properly?

Question

I'm wondering a user defined exception I've raised in my python program from within a class isn't being handled by the correct exception handler within my main() . Say I have a class:

class Pdbalog:
    # Constructor
    def __init__(self, logtype):
        if logtype == 1 or logtype == 2:
            # These are valid
            self.logtypeV = logtype
            ...<continue processing>
        else:
            # Invalid
            raise Exception("Invalid Logtype")

My main looks like:

from pdbalog import *
def main():
    try:
        mylog = Pdbalog(10)
        ...<other code here>

    except "Invalid Logtype":
        print('Exiting...')
    except:
        print('Unhandled exception')
        raise

I would expect the when main is run that the line where I instantiate the Pdbalog object would raise an exception ( Exception("Invalid Logtype") ) and the exception handler in main ( except "Invalid Logtype" ) would print the output string "Exiting..." . However, it does not. It is being handled by the unhandled exception handler. What ends up happening is the string "Unhandled exception" is being output. Why isn't the

    except "Invalid Logtype":

handling the exception?

I am using an old version of python (2.4).

Answer 1

Exception("Invalid Logtype") is still just an Exception , just now with an error message. "Invalid Logtype" isn't an error, just a str , so you can't catch it.

Try:

class InvalidLogtype(Exception): pass

try:
    raise InvalidLogType
except InvalidLogType:
    pass

Note that you can catch based on error messages by doing

except Exception, e:
    if e.args == ("Invalid Logtype",):
        ...

    else:
        raise

Answer 2

Try this instead:

class InvalidLogType(Exception):
   pass

then

raise InvalidLogType()

then

except InvalidLogType:
   etc