I ran into a bug in production unpickling some builtins (dicts or sets or something) that were pickled in 2.2 and unpickled in 2.4 (or 2.4 -> 2.6, it's fuzzy).

I ran into a bug in production unpickling some builtins (dicts or sets or something) that were pickled in 2.2 and unpickled in 2.4 (or 2.4 -> 2.6, it's fuzzy). Between those two versions, the exposed 'dunder' methods of whichever builtin changed, and this resulted in unpickled dicts being empty, IIRC.