My question about the idea is whether beginners would use this, or if it is the sort of 'expert' feature that IDLE should avoid.  I may ask on python-list for more opinions.

https://stackoverflow.com/questions/49677886/python-idle-symbol-completion/49684824#49684824 adds a vote in favor.  It also prompted me to review the patch.

Since I said, 4 years ago, that the feature should be an extension, we have converted extensions to features.  So the patch needs re-writing, as I outlined.

(Although there is now an extension configuration dialog, it is no longer a dependency of this issue.)

I am not convinced that we need 5 configuration options, especially since I do not understand 2 of them ;-).  Do symbol and quote fences need to be separately enabled?  Does anyone known what other IDEs do?