python exception handling

Question

In the below python the message RSU is not supported on single node machine** is not getting printed. can anyone help please??

#! /usr/bin/env python

import sys

class SWMException(Exception):
    def __init__(self, arg):
        print "inside exception"
        Exception.__init__(self, arg)

class RSUNotSupported(SWMException):
    def __init__(self):
        SWMException.__init__(self, "**RSU is not supported on single node machine**")

def isPrepActionNeeded():
    if 1==1:
        raise RSUNotSupported()
try:
    isPrepActionNeeded()
except:
    sys.exit(1)

Zaur Nasibov · Accepted Answer · 2011-08-11 07:18:10Z

2

It is not printed, because you're even not trying to print it :) Here:

try:
    isPrepActionNeeded()
except RSUNotSupported as e:
    print str(e)
    sys.exit(1)

answered Aug 11, 2011 at 7:18

Zaur Nasibov

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2 Comments

mandeep Over a year ago

Exception.__init__(self, arg) the arg passed here. what is that for??

Zaur Nasibov Over a year ago

Well, you do have to keep the "**RSU..." message somewhere, right? Your exception inherits from Exception class, thus Exception.__init__(self, message) initializes the superclass and passes the argument (the message) to it. Now, your exception contains that message, and calling __str__() of an RSUNotSupported class instance (or str( ) on that instance) returns the message.

wRAR · Accepted Answer · 2011-08-11 07:17:59Z

1

Because you handle the exception with your try/except clause.

answered Aug 11, 2011 at 7:17

wRAR

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Comments

agf · Accepted Answer · 2011-08-11 08:36:52Z

0

Change the last two lines to:

except Exception as e:
    print e
    sys.exit(1)

I use just Exception here to keep this the equivalent of a bare except:. You really should use RSUNotSupported so you don't hide other types of errors.

edited Aug 11, 2011 at 8:36

answered Aug 11, 2011 at 7:18

agf

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2 Comments

mandeep Over a year ago

Exception.__init__(self, arg) what is the arg argument in this init call for?? it doesnt print the message

agf Over a year ago

It's to make the message part of the exception, so you can print it yourself later if you want.

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