# Exception handling

def add_msg(e, msg): e.args = (str(e).rstrip()+'\n'+msg,)

def repl_msg(e, **repls): e.args = (str(e) % repls,)

class ExceptionWithCause(Exception):

    def __init__(self, msg, cause=None):

        Exception.__init__(self, msg)

        if cause != None: add_msg(self, 'cause: '+str(cause))