Raymond Hettinger <[email protected]> added the comment:
Just for the record, I wanted to highlight how little room there is for
optimization here. The sort wrapper is *very* thin:
sortwrapper_richcompare(sortwrapperobject *a, sortwrapperobject *b, int op)
{
if (!PyObject_TypeCheck(b, &PySortWrapper_Type)) {
PyErr_SetString(PyExc_TypeError,
"expected a sortwrapperobject");
return NULL;
}
return PyObject_RichCompare(a->key, b->key, op);
}
When a key function is defined, this is all you can possibly shave off the time
for a comparison. When a key function is not defined, there was no overhead at
all.
With the patch, we're relying on branch prediction to minimize the cost to the
regular case and adding a little indirection in the form of lo variables
becoming lo.keys, etc. And the number of memmoves is doubled.
To me, the main advantage of the patch is that it saves a little memory for
each key:
typedef struct {
PyObject_HEAD
PyObject *key;
PyObject *value;
} sortwrapperobject;
Just wanted to post this so there weren't any illusions about the patch being a
big win.
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<http://bugs.python.org/issue9915>
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