[Python-Dev] Inplace operations for PyLong objects (original) (raw)

Chris Barker chris.barker at noaa.gov
Sat Sep 2 13:38:05 EDT 2017

On Fri, Sep 1, 2017 at 6:16 PM, Joe Jevnik via Python-Dev < python-dev at python.org> wrote:

The string concat optimization happens in the interpreter dispatch for INPLACEADD

In that case, isn't there a new string being build, all in one line of python? that is, the string the optimization is being created at that point, so the interpreter can know there isn't anything referencing it anywhere else.

-CHB

On Fri, Sep 1, 2017 at 9:10 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:

Chris Angelico wrote:

This particular example is safe, because the arguments get passed individually - so 'args' has one reference, plus there's one more for the actual function call

However, that's also true when you use the += operator, so if the optimisation is to trigger at all in any useful case, the refcount threshold needs to be set higher than 1. Some experiments I did suggest that if you set it high enough for x += y to trigger it, then it will also be triggered in Joe's case. BTW, isn't there already a similar optimisation somewhere for concatenating strings? Does it still exist? How does it avoid this issue? -- Greg

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