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The patch no longer applies to trunk, but that would be trivial to fix.
Changes like these have been accepted with little resistance in the past 
(see e.g. issue651362), so I don't see why this patch has been pending 
for so long. (In general, I am -0 on adding const modifiers because 
they tend to trigger an avalanche of changes, but arguably this is the 
"right thing to do.") 
A few comments:
* Documentation needs to be updated in Doc/c-api/sys.rst. 
* Any reason why PySys_SetPath(char *) is left out?
* Same for PySys_SetArgv(int, char **)
* Similar changes are proposed in issue1772673. Maybe these two issues 
can be dealt with together.