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Mon Aug 22 04:01:38 EDT 2016 · https://mail.python.org/pipermail/python-dev/2016-August/145876.html

Hi,

I pushed the most basic implementation of _PyObject_FastCall(), it
doesn't support keyword parameters yet:
https://hg.python.org/cpython/rev/a1a29d20f52d
https://bugs.python.org/issue27128

Then I patched a lot of call sites calling PyObject_Call(),
PyObject_CallObject(), PyEval_CallObject(), etc. with a temporary
tuple. Just one example:

-            args = PyTuple_Pack(1, match);
-            if (!args) {
-                Py_DECREF(match);
-                goto error;
-            }
-            item = PyObject_CallObject(filter, args);
-            Py_DECREF(args);
+            item = _PyObject_FastCall(filter, &match, 1, NULL);

The next step is to support keyword parameters. In fact, it's already
supported in all cases except of Python functions:
https://bugs.python.org/issue27809

Supporting keyword parameters will allow to patch much code to avoid
temporary tuples, but it is also required for a much more interesting
change:
https://bugs.python.org/issue27810
"Add METH_FASTCALL: new calling convention for C functions"

I propose to add a new METH_FASTCALL calling convention. The example
using METH_VARARGS | METH_KEYWORDS:
   PyObject* func(DirEntry *self, PyObject *args, PyObject *kwargs)
becomes:
   PyObject* func(DirEntry *self, PyObject **args, int nargs, PyObject *kwargs)

Later, Argument Clinic will be modified to *generate* code using the
new METH_FASTCALL calling convention. Code written with Argument
Clinic will only need to be updated by Argument Clinic to get the new
faster calling convention (avoid the creation of a temporary tuple for
positional arguments).

Victor

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Showing content from https://mail.python.org/pipermail/python-dev/2016-August/145876.html below:

[Python-Dev] New calling convention to avoid temporarily tuples when calling functions