Question

I have code running on a server with namedtuples:

Event = namedtuple("Event", ['attr1', 'attr2', 'attr3'])

The server is getting events from other servers, coming out of a queue.

I want to add a new feature to my code which needs a new attribute in the namedtuple. Is there a good way to do this and keep backwards compatibility? That is, I can stop and start the server, and change the code to:

Event = namedtuple("Event", ['attr1', 'attr2', 'attr3', 'attr4'])

But in the meantime there will be Events with the old signature queued up.

Anyone done this before?

Answer 1

It would work as it is, only problem can occur is in your code when you are using the newly added attribute e.g.

from collections import namedtuple

Event1 = namedtuple("Event", ['attr1', 'attr2', 'attr3', 'attr4'])
Event2 = namedtuple("Event", ['attr1', 'attr2', 'attr3', 'attr4', 'attr5'])

def handle_event(event):
    print event.attr5

handle_event(Event2(1,2,3,4,5))
handle_event(Event1(1,2,3,4))

You will get error AttributeError: 'Event' object has no attribute 'attr5' so if you taken care of such thing in backward-compatible way, like checking if attr5 is there, it should work