Generalize PySequence_Count() (operator.countOf) to work with iterators.

Lib/test/test_iter.py

@@ -527,4 +527,39 @@ class TestCase(unittest.TestCase):
             except OSError:
                 pass
 
+    # Test iterators with operator.countOf (PySequence_Count).
+    def test_countOf(self):
+        from operator import countOf
+        self.assertEqual(countOf([1,2,2,3,2,5], 2), 3)
+        self.assertEqual(countOf((1,2,2,3,2,5), 2), 3)
+        self.assertEqual(countOf("122325", "2"), 3)
+        self.assertEqual(countOf("122325", "6"), 0)
+
+        self.assertRaises(TypeError, countOf, 42, 1)
+        self.assertRaises(TypeError, countOf, countOf, countOf)
+
+        d = {"one": 3, "two": 3, "three": 3, 1j: 2j}
+        for k in d:
+            self.assertEqual(countOf(d, k), 1)
+        self.assertEqual(countOf(d.itervalues(), 3), 3)
+        self.assertEqual(countOf(d.itervalues(), 2j), 1)
+        self.assertEqual(countOf(d.itervalues(), 1j), 0)
+
+        f = open(TESTFN, "w")
+        try:
+            f.write("a\n" "b\n" "c\n" "b\n")
+        finally:
+            f.close()
+        f = open(TESTFN, "r")
+        try:
+            for letter, count in ("a", 1), ("b", 2), ("c", 1), ("d", 0):
+                f.seek(0, 0)
+                self.assertEqual(countOf(f, letter + "\n"), count)
+        finally:
+            f.close()
+            try:
+                unlink(TESTFN)
+            except OSError:
+                pass
+
 run_unittest(TestCase)

Misc/NEWS

@@ -23,10 +23,12 @@ Core
     max()
     min()
     reduce()
+    tuple() (PySequence_Tuple() and PySequence_Fast() in C API)
     .join() method of strings
-    tuple()
+    'x in y' and 'x not in y' (PySequence_Contains() in C API)
+    operator.countOf() (PySequence_Count() in C API)
     XXX TODO zip()
-    'x in y' and 'x not in y'
+
 
 What's New in Python 2.1 (final)?
 =================================

Objects/abstract.c

@@ -1333,34 +1333,52 @@ PySequence_Fast(PyObject *v, const char *m)
 	return v;
 }
 
+/* Return # of times o appears in s. */
 int
 PySequence_Count(PyObject *s, PyObject *o)
 {
-	int l, i, n, cmp, err;
-	PyObject *item;
+	int n;  /* running count of o hits */
+	PyObject *it;  /* iter(s) */
 
 	if (s == NULL || o == NULL) {
 		null_error();
 		return -1;
 	}
-	
-	l = PySequence_Size(s);
-	if (l < 0)
+
+	it = PyObject_GetIter(s);
+	if (it == NULL) {
+		type_error(".count() requires iterable argument");
 		return -1;
+	}
 
 	n = 0;
-	for (i = 0; i < l; i++) {
-		item = PySequence_GetItem(s, i);
-		if (item == NULL)
-			return -1;
-		err = PyObject_Cmp(item, o, &cmp);
+	for (;;) {
+		int cmp;
+		PyObject *item = PyIter_Next(it);
+		if (item == NULL) {
+			if (PyErr_Occurred())
+				goto Fail;
+			break;
+		}
+		cmp = PyObject_RichCompareBool(o, item, Py_EQ);
 		Py_DECREF(item);
-		if (err < 0)
-			return err;
-		if (cmp == 0)
+		if (cmp < 0)
+			goto Fail;
+		if (cmp > 0) {
+			if (n == INT_MAX) {
+				PyErr_SetString(PyExc_OverflowError,
+				                "count exceeds C int size");
+				goto Fail;
+			}
 			n++;
+		}
 	}
+	Py_DECREF(it);
 	return n;
+
+Fail:
+	Py_DECREF(it);
+	return -1;
 }
 
 /* Return -1 if error; 1 if v in w; 0 if v not in w. */