Add the same _keep_alive patch (by Michael Scharff) that was added to copy.deepcopy() a while ago.  Can't reproduce this but it doesn't break anything and it looks like the code could have the same problem.
Add the same _keep_alive patch (by Michael Scharff) that was added to
copy.deepcopy() a while ago.  Can't reproduce this but it doesn't
break anything and it looks like the code could have the same problem.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator