Differences between revisions 1 and 12 (spanning 11 versions)

Writing Exception Classes

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         super(HostNotFound, self)('Host Not Found exception: missing %s' % host)

You may later write:

   1 try:
   2     raise HostNotFound("taoriver.net")
   3 except HostNotFound, exc:
   4     # Handle exception.
   5     print exc  # -> 'Host Not Found exception: missing taoriver.net'
   6     print exc.host  # -> 'taoriver.net'

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. -- LionKimbro DateTime(2003-09-07T15:23:43Z)
Look at cgitb for how to do detailed TB introspection, and as an example of why mixing logic and (HTML) layout is a very bad thing.
What better exception-foo is out there?
AlexMartelli's "Dos and Don'ts".

-  ⇤ ← Revision 1 as of 2003-09-06 18:34:16 → 
  Size: 1097
  Editor: dsl254-010-130
  Comment: Initial version, Req for Comment.
+   ← Revision 12 as of 2004-08-25 04:59:45 → ⇥
  Size: 1270
  Editor: cpe-68-112-255-10
  Comment: Updated example to use super()
-Deletions are marked like this.
+Additions are marked like this.
 Line 3:
-I (LionKimbro) don't know much about writing exception classes; Here's hoping someone rewrites this better.

Exception classes are not special; You just write an ordinary class:
+Exception classes are not special, you just derive them from Exception:
-Line 9:
+Line 7:
-class HostNotFound:
    def __init__( self, host ):
+class HostNotFound(Exception):
    def __init__(self, host):
-Line 12:
+Line 10:
+        super(HostNotFound, self)('Host Not Found exception: missing %s' % host)
-Line 19:
+Line 18:
-    raise HostNotFound( "taoriver.net" )
except HostNotFound, X:
    print "Host Not Found:", X.host
+    raise HostNotFound("taoriver.net")
except HostNotFound, exc:
    # Handle exception.
    print exc  # -> 'Host Not Found exception: missing taoriver.net'
    print exc.host  # -> 'taoriver.net'
-Line 24:
+Line 26:
-== Overloading __str__ ==
+== See Also ==
-Line 26:
+Line 28:
-You can overload {{{__str__}}} to get the exception to explain itself:

{{{
#!python
class HostNotFound:
    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.
+HandlingExceptions, TracebackModule
-Line 51:
+Line 32:
-  * How do you relay the traceback information?
+  * 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. -- LionKimbro [[DateTime(2003-09-07T15:23:43Z)]]

  ''Look at cgitb for how to do detailed TB introspection, and as an example of why mixing logic and (HTML) layout is a very bad thing.''
-Line 53:
+Line 38:
+  ''AlexMartelli's "Dos and Don'ts".''

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Writing Exception Classes

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