newbie question - exception processing

[M.E.Farmer]

mirandacascade at yahoo.com wrote:
> O/S: Windows XP Service Pack 2
> Python version: 2.4
>
> Unable to understand how to build a class to handle an exception.
>
> Contents of sample01.py:
> import exceptions
> class SampleMain:
>     try:
>         def __init__(self):
>             print 'in SampleMain constructor'
>
>         def Allowed(self):
>             print 'in allowed'
>
>         def NotYetAllowed(self):
>             UCError = UnderConstructionError('not yet ready')
>             raise UCError
>
>     except UnderConstructionError, e:
>         print e.msg
>
> class Error(exceptions.Exception):
>     def __init__(self):
>         print 'in base class constructor'
>
> class UnderConstructionError(Error):
>     def __init__(self, message):
>         print 'in UnderConstructionError constructor'
>         self.msg = message
>
> Copy/paste of interactive window:
> PythonWin 2.4 (#60, Nov 30 2004, 09:34:21) [MSC v.1310 32 bit
(Intel)]
> on win32.
> Portions Copyright 1994-2004 Mark Hammond (mhammond at skippinet.com.au)
-
> see 'Help/About PythonWin' for further copyright information.
> >>> import sample01
> >>> x = sample01.SampleMain()
> in SampleMain constructor
> >>> x.NotYetAllowed()
> in UnderConstructionError constructor
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
>   File "C:\Python24\sample01.py", line 12, in NotYetAllowed
>     raise UCError
> UnderConstructionError: <unprintable instance object>
> >>>
>
> My questions are:
> 1) What is causing the error described in the Traceback?
> 2) Given that what I want to happen when the NotYetAllowed() method
is
> called is:
>     a) an exception to be raised
>     b) the exception results in a message getting printed; the
message
> should come from the place where the exception was raised, and it
> should be passed to the exception class as a string object; so in
this
> case the message that should be printed is 'not yet ready'
>     c) the exception gets handled with the try/except within the
> SampleMain class
>
> My question is: what changes must I make to the code to make that
> happen?
>
> Thank you.
Hello ,
This is originally snagged from the standard library.
Spend time reading thru the modules they will show you how to do a lot
of things.
# Exception example
class PSCError(Exception):
    # Base for custom errors
    def __init__(self, msg=''):
        self._msg = msg
        Exception.__init__(self, msg)
    def __repr__(self):
        return self._msg
    __str__ = __repr__

class PathError(PSCError):
    def __init__(self, msg):
       PSCError.__init__(self,
         'Path error! : %s'% msg)

class InputError(PSCError):
   def __init__(self, msg):
       PSCError.__init__(self,
         'Input error! : %s'% msg)

# and you use it like this
raise PathError, 'Please check path'
raise InputError, 'Improper input try again'

hth,
M.E.Farmer