Generalize max(seq) and min(seq) to work with iterators.

NEEDS DOC CHANGES.

Lib/test/test_iter.py

@@ -319,4 +319,39 @@ class TestCase(unittest.TestCase):
         self.assertEqual(filter(lambda x: not x, seq), [False]*25)
         self.assertEqual(filter(lambda x: not x, iter(seq)), [False]*25)
 
+    # Test max() and min()'s use of iterators.
+    def test_builtin_max_min(self):
+        self.assertEqual(max(SequenceClass(5)), 4)
+        self.assertEqual(min(SequenceClass(5)), 0)
+        self.assertEqual(max(8, -1), 8)
+        self.assertEqual(min(8, -1), -1)
+
+        d = {"one": 1, "two": 2, "three": 3}
+        self.assertEqual(max(d), "two")
+        self.assertEqual(min(d), "one")
+        self.assertEqual(max(d.itervalues()), 3)
+        self.assertEqual(min(iter(d.itervalues())), 1)
+
+        self.assertRaises(TypeError, list, list)
+        self.assertRaises(TypeError, list, 42)
+
+        f = open(TESTFN, "w")
+        try:
+            f.write("medium line\n")
+            f.write("xtra large line\n")
+            f.write("itty-bitty line\n")
+        finally:
+            f.close()
+        f = open(TESTFN, "r")
+        try:
+            self.assertEqual(min(f), "itty-bitty line\n")
+            f.seek(0, 0)
+            self.assertEqual(max(f), "xtra large line\n")
+        finally:
+            f.close()
+            try:
+                unlink(TESTFN)
+            except OSError:
+                pass
+
 run_unittest(TestCase)

Misc/NEWS

@@ -19,6 +19,8 @@ Core
   arguments:
     filter()
     list()
+    max()
+    min()
 
 
 What's New in Python 2.1 (final)?

Python/bltinmodule.c

@@ -1444,30 +1444,37 @@ static PyObject *
 min_max(PyObject *args, int op)
 {
 	int i;
-	PyObject *v, *w, *x;
-	PySequenceMethods *sq;
+	PyObject *v, *w, *x, *it;
 
 	if (PyTuple_Size(args) > 1)
 		v = args;
 	else if (!PyArg_ParseTuple(args, "O:min/max", &v))
 		return NULL;
-	sq = v->ob_type->tp_as_sequence;
-	if (sq == NULL || sq->sq_item == NULL) {
-		PyErr_SetString(PyExc_TypeError,
-				"min() or max() arg must be a sequence");
+	
+	it = PyObject_GetIter(v);
+	if (it == NULL)
 		return NULL;
-	}
-	w = NULL;
+
+	w = NULL;  /* the result */
 	for (i = 0; ; i++) {
-		x = (*sq->sq_item)(v, i); /* Implies INCREF */
+		x = PyIter_Next(it);
 		if (x == NULL) {
-			if (PyErr_ExceptionMatches(PyExc_IndexError)) {
-				PyErr_Clear();
-				break;
+			/* We're out of here in any case, but if this is a
+			 * StopIteration exception it's expected, but if
+			 * any other kind of exception it's an error.
+			 */
+			if (PyErr_Occurred()) {
+				if (PyErr_ExceptionMatches(PyExc_StopIteration))
+					PyErr_Clear();
+				else {
+					Py_XDECREF(w);
+					Py_DECREF(it);
+					return NULL;
+				}
 			}
-			Py_XDECREF(w);
-			return NULL;
+			break;
 		}
+
 		if (w == NULL)
 			w = x;
 		else {
@@ -1478,7 +1485,8 @@ min_max(PyObject *args, int op)
 			}
 			else if (cmp < 0) {
 				Py_DECREF(x);
-				Py_XDECREF(w);
+				Py_DECREF(w);
+				Py_DECREF(it);
 				return NULL;
 			}
 			else
@@ -1488,6 +1496,7 @@ min_max(PyObject *args, int op)
 	if (w == NULL)
 		PyErr_SetString(PyExc_ValueError,
 				"min() or max() arg is an empty sequence");
+	Py_DECREF(it);
 	return w;
 }