Differences between revisions 5 and 6

Writing Exception Classes

I (LionKimbro) don't know much about writing exception classes; Here's hoping someone rewrites this better.

Exception classes are not special, you just derive them from Exception:

   1 class HostNotFound(Exception):
   2     def __init__( self, host ):
   3         self.host = host
   4         Exception.__init__(self, 'Host Not Found exception: missing %s' % host)

You may later write:

Toggle line numbers

   1 try:
   2     raise HostNotFound( "taoriver.net" )
   3 except HostNotFound, X:
   4     # Handle exception.
   5     # "X" is the HostNotFound instance.

Questions

How do you relay the traceback information? Relay the traceback information? Moving it higher up the call-stack? Could you try to explain your question?
- When you're logging exceptions, you want access to the traceback information to. After some research, I believe what you use is extract_tb or extract_stack from the traceback module. -- 216.254.10.130 DateTime(2003-09-07T15:23:43Z)
What better exception-foo is out there?

-  ⇤ ← Revision 5 as of 2003-09-07 11:16:23 → 
  Size: 1591
  Editor: ip503dabc3
  Comment:
+   ← Revision 6 as of 2003-09-07 15:23:43 → ⇥
  Size: 1125
  Editor: dsl254-010-130
  Comment: __str__ section no longer necessary, answered question, added "See Also".
-Deletions are marked like this.
+Additions are marked like this.
 Line 12:
-        Exception.__init__(self)
+        Exception.__init__(self, 'Host Not Found exception: missing %s' % host)
 Line 22:
-    print "Host Not Found:", X.host
+    # Handle exception.
    # "X" is the HostNotFound instance.
-Line 25:
+Line 26:
-== Overloading __str__ ==
+== See Also ==
-Line 27:
+Line 28:
-You can overload {{{__str__}}} to get the exception to explain itself:

{{{
#!python
class HostNotFound(Exception):
    def __init__( self, host ):
        self.host = host
    def __str__( self ):
        return "Host Not Found exception: missing %s" % self.host
}}}

That way, you only need print the exception instance:

{{{
#!python
try:
    raise HostNotFound( "taoriver.net" )
except HostNotFound, X:
    print X
}}}

I don't know if this is a good idea or not.

''In this instance, there's no need to overload {{{__str__}}}, as the standard Exception already has a {{{__str__}}} method:''

{{{
#!python
class HostNotFound(Exception):
    def __init__(self, host):
        self.host = host
        Exception.__init__(self, 'Host Not Found exception: missing %s' % host)
}}}
+HandlingExceptions, TracebackModule
-Line 63:
+Line 33:
+     * When you're logging exceptions, you want access to the traceback information to. After some research, I believe what you use is extract_tb or extract_stack from the traceback module. -- 216.254.10.130 [[DateTime(2003-09-07T15:23:43Z)]]

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Writing Exception Classes

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