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On 2018-04-01 20:10, Terry Reedy wrote:
On 4/1/2018 8:36 AM, Steven D'Aprano wrote:
On Sun, Apr 01, 2018 at 08:08:41AM -0400, Richard Damon wrote:
One comment about the 'combinatorial explosion' is that it sort of assumes that each individual combination case needs to be handled with distinct code.
No -- as I said in an earlier post, Terry and I (and Eric) are talking about the explosion in number of prefixes, not the complexity of the code.
You are right that many of the prefixes can be handled by the same code:
rfd rfD rFd rFD rdf rdF rDf rDF Rfd RfD RFd RFD Rdf RdF RDf RDF frd frD fRd fRD fdr fdR fDr fDR Frd FrD FRd FRD Fdr FdR FDr FDR drf drF dRf dRF dfr dfR dFr dFR Drf DrF DRf DRF Dfr DfR DFr DFR # why did we support all these combinations? who uses them?
presumably will all handled by the same "raw dedent f-string" code. But the parser still has to handle all those cases, and so does the person reading the code.
IDLE's colorizer does its parsing with a giant regex. The new prefix combinations would nearly double the number of alternatives in the regex. I am sure that this would mean more nodes in the compiled finite-state machine. Even though the non-re code of the colorizer would not change, I am pretty sure that this would mean that coloring takes longer. Since the colorizer is called with each keystroke, and since other events can be handled between keystrokes#, colorizing timecould* become an issue, especially on older or slower machines than mine. Noticeable delays between keystroke and character appearance on screen are a real drag.
In Python 3.7 that part is now:
stringprefix = r"(?i:\br|u|f|fr|rf|b|br|rb)?"
(which looks slightly wrong to me!).