Issue #21424: Optimize heaqp.nlargest() to make fewer tuple comparisons.

Consolidates the logic for nlargest() into a single function so that
decoration tuples (elem,order) or (key, order, elem) only need to
be formed when a new element is added to the heap.  Formerly, a tuple
was created for every element regardless of whether it was added to
the heap.

The change reduces the number of tuples created, the number of ordering
integers created, and total number of tuple comparisons.

1 files changed, 0 insertions, 85 deletions

diff --git a/Modules/_heapqmodule.c b/Modules/_heapqmodule.c
index b3e4753f265..964f5116469 100644
--- a/Modules/_heapqmodule.c
+++ b/Modules/_heapqmodule.c
@@ -267,89 +267,6 @@ heapify(PyObject *self, PyObject *heap)
 PyDoc_STRVAR(heapify_doc,
 "Transform list into a heap, in-place, in O(len(heap)) time.");
 
-static PyObject *
-nlargest(PyObject *self, PyObject *args)
-{
-    PyObject *heap=NULL, *elem, *iterable, *sol, *it, *oldelem;
-    Py_ssize_t i, n;
-    int cmp;
-
-    if (!PyArg_ParseTuple(args, "nO:nlargest", &n, &iterable))
-        return NULL;
-
-    it = PyObject_GetIter(iterable);
-    if (it == NULL)
-        return NULL;
-
-    heap = PyList_New(0);
-    if (heap == NULL)
-        goto fail;
-
-    for (i=0 ; i<n ; i++ ){
-        elem = PyIter_Next(it);
-        if (elem == NULL) {
-            if (PyErr_Occurred())
-                goto fail;
-            else
-                goto sortit;
-        }
-        if (PyList_Append(heap, elem) == -1) {
-            Py_DECREF(elem);
-            goto fail;
-        }
-        Py_DECREF(elem);
-    }
-    if (PyList_GET_SIZE(heap) == 0)
-        goto sortit;
-
-    for (i=n/2-1 ; i>=0 ; i--)
-        if(_siftup((PyListObject *)heap, i) == -1)
-            goto fail;
-
-    sol = PyList_GET_ITEM(heap, 0);
-    while (1) {
-        elem = PyIter_Next(it);
-        if (elem == NULL) {
-            if (PyErr_Occurred())
-                goto fail;
-            else
-                goto sortit;
-        }
-        cmp = PyObject_RichCompareBool(sol, elem, Py_LT);
-        if (cmp == -1) {
-            Py_DECREF(elem);
-            goto fail;
-        }
-        if (cmp == 0) {
-            Py_DECREF(elem);
-            continue;
-        }
-        oldelem = PyList_GET_ITEM(heap, 0);
-        PyList_SET_ITEM(heap, 0, elem);
-        Py_DECREF(oldelem);
-        if (_siftup((PyListObject *)heap, 0) == -1)
-            goto fail;
-        sol = PyList_GET_ITEM(heap, 0);
-    }
-sortit:
-    if (PyList_Sort(heap) == -1)
-        goto fail;
-    if (PyList_Reverse(heap) == -1)
-        goto fail;
-    Py_DECREF(it);
-    return heap;
-
-fail:
-    Py_DECREF(it);
-    Py_XDECREF(heap);
-    return NULL;
-}
-
-PyDoc_STRVAR(nlargest_doc,
-"Find the n largest elements in a dataset.\n\
-\n\
-Equivalent to:  sorted(iterable, reverse=True)[:n]\n");
-
 static int
 _siftdownmax(PyListObject *heap, Py_ssize_t startpos, Py_ssize_t pos)
 {
@@ -531,8 +448,6 @@ static PyMethodDef heapq_methods[] = {
         METH_VARARGS,           heapreplace_doc},
     {"heapify",         (PyCFunction)heapify,
         METH_O,                 heapify_doc},
-    {"nlargest",        (PyCFunction)nlargest,
-        METH_VARARGS,           nlargest_doc},
     {"nsmallest",       (PyCFunction)nsmallest,
         METH_VARARGS,           nsmallest_doc},
     {NULL,              NULL}           /* sentinel */