python: How do I know what type of exception occurred?

Question

I have a function called by the main program:

try:
    someFunction()
except:
    print \"exception happened!\"

but in the middle of the ex

Answer 1

Get the name of the class that exception object belongs:

e.__class__.__name__

and using print_exc() function will also print stack trace which is essential info for any error message.

Like this:

from traceback import print_exc

class CustomException(Exception): pass

try:
    raise CustomException("hi")
except Exception, e:
    print 'type is:', e.__class__.__name__
    print_exc()
    # print "exception happened!"

You will get output like this:

type is: CustomException
Traceback (most recent call last):
  File "exc.py", line 7, in 
    raise CustomException("hi")
CustomException: hi

And after print and analysis, the code can decide not to handle exception and just execute raise:

from traceback import print_exc

class CustomException(Exception): pass

def calculate():
    raise CustomException("hi")

try:
    calculate()
except Exception, e:
    if e.__class__ == CustomException:
        print 'special case of', e.__class__.__name__, 'not interfering'
        raise
    print "handling exception"

Output:

special case of CustomException not interfering

And interpreter prints exception:

Traceback (most recent call last):
  File "test.py", line 9, in 
    calculate()
  File "test.py", line 6, in calculate
    raise CustomException("hi")
__main__.CustomException: hi

After raise original exception continues to propagate further up the call stack. (Beware of possible pitfall) If you raise new exception it caries new (shorter) stack trace.

from traceback import print_exc

class CustomException(Exception): pass

def calculate():
    raise CustomException("hi")

try:
    calculate()
except Exception, e:
    if e.__class__ == CustomException:
        print 'special case of', e.__class__.__name__, 'not interfering'
        #raise CustomException(e.message)
        raise e
    print "handling exception"

Output:

special case of CustomException not interfering
Traceback (most recent call last):
  File "test.py", line 13, in 
    raise CustomException(e.message)
__main__.CustomException: hi    

Notice how traceback does not include calculate() function from line 9 which is the origin of original exception e.