Python - Conditionally Catching Exceptions

You can re-raise the exception if you don't want to handle it:

def my_func(my_arg, handle_exceptions):
    try:
        do_something(my_arg)
    except Exception, e:
        if not handle_exceptions:
            # preserve prior stack trace
            raise

            # Or, if you dont care about the stack prior to this point
            #raise Exception(e)

            # similarly, you can just re-raise e.  The stack trace will start here though.
            #raise e
        else:
            print "my_func is handling the exception"

---

Another option is to create your own exceptions that subclass Exception (or a specific exception like urllib2.HTTPError) and then only catch/throw (raise) your custom exception:

class MyException(Exception):
    def __init__(self, message):
        self.message = message

class MyExceptionTwo(Exception):
    def __init__(self, message):
        self.message = message
    def __repr__(self):
        return "Hi, I'm MyExceptionTwo.  My error message is: %s" % self.message

def something():
    if not tuesday:
        raise MyException("Error: it's not Tuesday.")
    else:
        raise MyExceptionTwo("Error: it's Tuesday.")

def my_func(my_arg):
    try:
        something()
    except MyException, e:
        print e.message
    # Will pass MyExceptionTwo up the call chain

def my_other_func():
    try:
        my_func(your_arg)
    except MyExceptionTwo, e:
        print str(e)
    # No need to catch MyException here since we know my_func() handles it
    # but we can hadle MyExceptionTwo here

The question just doesn't have enough answers ;-)

Here's one more for the record books. Just create a dummy exception:

class NeverMatch(Exception):
    'An exception class that is never raised by any code anywhere'

Then, use a conditional expression to decide whether to match the real exception or the placeholder exception (which never gets raised):

try:
    do_something(my_arg)
except (Exception if handle_exceptions else NeverMatch) as e:
    print 'I am handling it'

You can use:

def my_func(my_arg, handle_exceptions):
  try:
    do_something(my_arg);
  except Exception as e:
    if not handle_exceptions: raise
    print "my_func is handling the exception";