The patch is trivial, and I assume that the test change is adequate, but I want to put this issue on hold for the present because
a) the performance gain is minuscule (the code cleanup is worth a bit more);
b) I am reluctant to backport something to 3.6 that depends on an unofficial implementation change, but not doing so will make backports of changes in this area not automatic;
c) I think I want to switch the browsers to ttk.Treeview, I hope before 3.6 goes off maintenance, and I expect that doing so will change this area of the code, and possibly the line being changed.

'The present' ends when 3.6 maintenance ends in 6 months or at least the module browser is patched, whichever is first.