rule._byweekday as set broke backward compatibility

[pypingou]

rule._byweekday used to be a list and moving it to a set broke backward compatibility.

For example, vobject no longer works with the most recent dateutil, backtrace available at:
http://jenkins.cloud.fedoraproject.org/job/fedocal/456/console

[ralphbean]

Attributes that begin with a _ are generally considered "private" and not part of a public API. So I wouldn't call it a break in backwards compatibility and instead call it a bug in that vobject library.

[pganssle]

I agree with @ralphbean. vObject shouldn't be directly accessing private variables like that. Additionally, I'm fairly certain that rrule._byweekday used to be a tuple not a list.

@pypingou Is there no way to do what vObject is trying to do using the publicly exposed methods and functions? If not, maybe the solution is to add a public interface to some of these internal variables so that your use case is officially supported.

That said, it's not critical that these things be stored as sets, it just makes certain operations faster and it's the more natural way to store them (since they are unique and there's no reason for them to be ordered). If this is going to cause widespread compatibility problems, we can probably make them tuple again for now, and push all potentially breaking changes to the switch over to rrule2 described in Issue #15.

[pypingou]

Thanks for your feedbacks, I think that in fact the much larger problem is the fact that vobject is pretty much dead upstream with no real project providing the same functionality (icalendar isn't complete iirc).

I will look if I can do something on the vobject side, which I think is the better long-term solution.

[jarondl]

Well put @pganssle.
I am closing as wontfix.

relvant link: http://xkcd.com/1172/