'''
Some utility classes for exception handling of exceptions raised
within listeners:
- IExcHandler: base class for any handler that would be given to
pub.setListenerExcHandler(). The derived class will probably
want to make use of TracebackInfo.
- TracebackInfo: convenient way of getting stack trace of latest
exception raised. The handler can create the instance to retrieve
the stack trace and then log it, present it to user, etc.
- ExcPublisher: example handler that publishes a message containing
traceback info
:copyright: Copyright 2006-2009 by Oliver Schoenborn, all rights reserved.
:license: BSD, see LICENSE.txt for details.
'''
import sys, traceback
class TracebackInfo:
'''
Represent the traceback information for when an exception is
raised -- but not caught -- in a listener. The complete
traceback cannot be stored since this leads to circular
references (see docs for sys.exc_info()) which keeps
listeners alive even after the application is no longer
referring to them.
Instances of this object are given to listeners of the
'uncaughtExcInListener' topic as the excTraceback kwarg.
The instance calls sys.exc_info() to get the traceback
info but keeps only the following info:
* self.ExcClass: the class of exception that was raised and not caught
* self.excArg: the argument given to exception when raised
* self.traceback: list of quadruples as returned by traceback.extract_tb()
Normally you just need to call one of the two getFormatted() methods.
'''
def __init__(self):
tmpInfo = sys.exc_info()
self.ExcClass = tmpInfo[0]
self.excArg = tmpInfo[1]
# for the traceback, skip the first 3 entries, since they relate to
# implementation details for pubsub.
self.traceback = traceback.extract_tb(tmpInfo[2])[3:]
# help avoid circular refs
del tmpInfo
def getFormattedList(self):
'''Get a list of strings as returned by the traceback module's
format_list() and format_exception_only() functions.'''
tmp = traceback.format_list(self.traceback)
tmp.extend( traceback.format_exception_only(self.ExcClass, self.excArg) )
return tmp
def getFormattedString(self):
'''Get a string similar to the stack trace that gets printed
to stdout by Python interpreter when an exception is not caught.'''
return ''.join(self.getFormattedList())
def __str__(self):
return self.getFormattedString()
class IExcHandler:
'''
Interface class for the exception handler. Such handler is called
whenever a listener raises an exception during a pub.sendMessage().
You may give an instance of a class derived from IExcHandlerto import
pub.setListenerExcHandler(). Example::
from pubsub.utils.exchandling import IExcHandler
class MyHandler(IExcHandler):
def __call__(self, listenerID, topicObj):
... do something with listenerID ...
'''
def __call__(self, listenerID, topicObj):
raise NotImplementedError('%s must override __call__()' % self.__class__)
class ExcPublisher(IExcHandler):
'''
Example exception handler that simply publishes the exception traceback.
The topic used will be self.topicUncaughtExc.
'''
# name of the topic
topicUncaughtExc = 'uncaughtExcInListener'
def __init__(self, topicMgr=None):
'''If topic manager is specified, will automatically call init().
Otherwise, caller must call init() after pubsub imported. See
pub.setListenerExcHandler().'''
if topicMgr is not None:
self.init(topicMgr)
def init(self, topicMgr):
'''Must be called only after pubsub has been imported since this
handler creates a pubsub topic.'''
obj = topicMgr.getOrCreateTopic(self.topicUncaughtExc)
obj.setDescription('generated when a listener raises an exception')
obj.setMsgArgSpec( dict(
listenerStr = 'string representation of listener',
excTraceback = 'instance of TracebackInfo containing exception info'))
self.__topicObj = obj
def __call__(self, listenerID, topicObj):
'''Handle the exception raised by given listener. Send the
Traceback to all subscribers of topic self.topicUncaughtExc. '''
tbInfo = TracebackInfo()
self.__topicObj.publish(listenerStr=listenerID, excTraceback=tbInfo)
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