[Python-Dev] Re-introduce caching for _strptime.py for 2.3.1?

[Brett C.]

Bug #780807 is a complaint that strptime is now 1,200 times slower than 
a C library version the user used to have.  Now slowdown is going to 
happen since Python string code can't compete with C string code, let 
alone _strptime has to figure out the locale info it needs while a C 
version has direct access.  And I am sure people who now have strptime 
on their platform are not going to complain about performance.  =)

But 1,200 times is a little high.  The new version I checked into HEAD 
is supposedly only 3 times slower than the equivalant C version 
according to the bug report submitter.  This is mainly because of caching.

My question is whether I should backport any of this.  The new version 
of _strptime is thread-safe and has caching (2.3 is already thread-safe 
thanks to the loss of caching for that version).  If I were to 
re-introduce caching (which was in 2.3 until a day before 2.3.0c2) I 
would need to also tweak other code to keep it thread-safe.  In other 
words I would have to do more work than just throw back in the caching 
code with the addition of a thread lock.

Is this considered a bugfix?  The only reason I question whether it is 
since it is not a pure "bugfix" is because I know at least Raymond 
thought the code should have gone back in before 2.3.0 final went out. 
Had I not been so panicked about fixing that one bug the caching code 
would still be in there and I would be patching 2.3.1 to make it 
thread-safe instead of sending out this email.

-Brett