Comparing Exception Objects in Python

Question

I am new at Python and I'm stuck at this problem. I am trying to compare two "exception objects", example:

try:
    0/0
except Exception as e:
    print e
>> integer division or modulo by zero

try:
    0/0
except Exception as e2:
    print e2
>> integer division or modulo by zero

e == e2
>> False

e is e2
>> False

How should I perform this comparison to obtain a "True"?

What I am trying to do:

class foo():
    def bar(self, oldError = None):
        try:
            return urllib2.urlopen(someString).read()                   
        except urllib2.HTTPError as e:
            if e.code == 400: 
               if e != oldError: print 'Error one'
            else: 
               if e != oldError: print "Error two"
            raise
         except urllib2.URLError as e:
             if e != oldError: print 'Error three'
             raise

class someclass():        
    # at some point this is called as a thread
    def ThreadLoop(self, stopThreadEvent):
        oldError = None
        while not stopThreadEvent.isSet():
            try:
                a = foo().bar(oldError = oldError)
            except Exception as e:
                oldError = e
            stopThreadEvent.wait(3.0)

(probably some syntax error)

Why I am doing that? Because I don't want to print the same error twice

Answer 1

With most exception classes, you can test for functional equality with

type(e) is type(e2) and e.args == e2.args

This tests that their classes are exactly identical, and that they contain the same exception arguments. This may not work for exception classes that don't use args, but to my knowledge, all standard exceptions do.

Answer 2

You want to check the type of the exception:

>>> isinstance(e2, type(e))
True

Note, naturally, this will allow for subclasses - this is a weird thing to do, so I'm not sure what behaviour you are looking for.