After-thought test 2: proportional fonts* work fine.  Nearly all have monospaced digits, with extra space around '1' if there is no bottom bar.  So those also have nicely aligned right-justified columns in the sidebar.  And the one font I found with proportional digits, Miriam Libre, still had readable numbers.

* Given the PEP 8 discouragement of the sort of vertical alignment, such as

one      =  1
eight    =  8
ten      = 10
nineteen = 19

which people, including me, have done with other languages, using a proportional font with python is not nearly as crazy as some people claim, and not to be totally disregarded.  The main issue is line length and what happens when someone else views the same file with a fixed-pitch font.