The tentative optimism in Europe contrasts with the news from the U. S., where there is mounting evidence that the already sluggish recovery has lost momentum.
The good news is that we've made a lot of the mistakes already and we've learned some lessons (see this technical rant, this post-mortem or this experiment).
In anticipation of lower demand for bonds from the Fed, they have been driving up the yields on U. S. Treasurys, which rose to their highest level in a month.
Once you are sure that all the existing instances have been unpickled, updated, and re-pickled, you can remove the old class definition from the source code module.