id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	launchpad_bug
2373	adopt pyrsistent	zooko		"https://warehouse.python.org/project/pyrsistent/

Immutable data structures. They reduce bugs by avoiding the situation where someone mutates a data structure that someone else was counting on to stay the same. We already try to use `frozenset` instead of `set` or `dict`, where-ever we can, but the pyrsistent library also adds immutable dicts and many other useful tools. I still remember staying up all night with Daira one time tracking down a bug just before the Tahoe-LAFS v1.8 release, which turned out to be an accidentally-mutated dict…

One huge drawback to adopting this, of course, is that it is another dependency. However, it is pure-Python and I don't think they're going to be making backwards-incompatible changes to the API, so it is a lot less costly than some of our dependencies."	enhancement	new	normal	undecided	unknown	1.10.0