Exception Handling in Python

quoted directly from Doug Hellman

#!/usr/bin/env python

import sys
import traceback

def throws():
    raise RuntimeError('error from throws')
    
def nested():
    try:
        throws()
    except Exception, original_error:
        try:
            raise
        finally:
            try:
                cleanup()
            except:
                pass # ignore errors in cleanup

def cleanup():
    raise RuntimeError('error from cleanup')

def main():
    try:
        nested()
        return 0
    except Exception, err:
        traceback.print_exc()
        return 1

if __name__ == '__main__':
    sys.exit(main())

This construction prevents the original exception from being overwritten by the latter, and preserves the full stack in the traceback.