Add count() method to collections.deque().

diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index aa17a559da47e2c46794dec258ba5f292014e618..3d04063adee8c32b0037212e50362fa670270ea1 100644 (file)
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -338,6 +338,12 @@ counts, but the output will exclude results with counts of zero or less.
       Remove all elements from the deque leaving it with length 0.
 
 
+   .. method:: count(x)
+
+      Count the number of deque elements equal to *x*.
+
+      .. versionadded:: 3.2
+
    .. method:: extend(iterable)
 
       Extend the right side of the deque by appending elements from the iterable

diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index a2f5fae9d64740795e14826a17cbe3552b673d49..17d724c5fa0b5d96d13964825def4f880309c0d6 100644 (file)
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -114,6 +114,30 @@ class TestBasic(unittest.TestCase):
             d = deque('abc')
             d.maxlen = 10
 
+    def test_count(self):
+        for s in ('', 'abracadabra', 'simsalabim'*500+'abc'):
+            s = list(s)
+            d = deque(s)
+            for letter in 'abcdefghijklmnopqrstuvwxyz':
+                self.assertEqual(s.count(letter), d.count(letter), (s, d, letter))
+        self.assertRaises(TypeError, d.count)       # too few args
+        self.assertRaises(TypeError, d.count, 1, 2) # too many args
+        class BadCompare:
+            def __eq__(self, other):
+                raise ArithmeticError
+        d = deque([1, 2, BadCompare(), 3])
+        self.assertRaises(ArithmeticError, d.count, 2)
+        d = deque([1, 2, 3])
+        self.assertRaises(ArithmeticError, d.count, BadCompare())
+        class MutatingCompare:
+            def __eq__(self, other):
+                self.d.pop()
+                return True
+        m = MutatingCompare()
+        d = deque([1, 2, 3, m, 4, 5])
+        m.d = d
+        self.assertRaises(RuntimeError, d.count, 3)
+
     def test_comparisons(self):
         d = deque('xabc'); d.popleft()
         for e in [d, deque('abc'), deque('ab'), deque(), list(d)]:

diff --git a/Misc/NEWS b/Misc/NEWS
index e042975d78a3445dd18a223f91ec13bf2d4f1e1c..7c23e26425c8cf59328e92cca2331970f6843d88 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -576,7 +576,7 @@ Library
 - Issue #5949: added check for correct lineends in input from IMAP server
   in imaplib.
 
-- Add a reverse() method to collections.deque().
+- Add count() and reverse() methods to collections.deque().
 
 - Fix variations of extending deques:  d.extend(d)  d.extendleft(d)  d+=d
 

diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index ffb2a8066d94243da08391a0ee1c9bbd1ad59a22..fa0f004989f073e9bb61548522a9900357a5a6d3 100644 (file)
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -504,6 +504,46 @@ deque_reverse(dequeobject *deque, PyObject *unused)
 PyDoc_STRVAR(reverse_doc,
 "D.reverse() -- reverse *IN PLACE*");
 
+static PyObject *
+deque_count(dequeobject *deque, PyObject *v)
+{
+       block *leftblock = deque->leftblock;
+       Py_ssize_t leftindex = deque->leftindex;
+       Py_ssize_t n = (deque->len);
+       Py_ssize_t i;
+       Py_ssize_t count = 0;
+       PyObject *item;
+       long start_state = deque->state;
+       int cmp;
+
+       for (i=0 ; i<n ; i++) {
+               item = leftblock->data[leftindex];
+               cmp = PyObject_RichCompareBool(item, v, Py_EQ);
+               if (cmp > 0)
+                       count++;
+               else if (cmp < 0)
+                       return NULL;
+
+               if (start_state != deque->state) {
+                       PyErr_SetString(PyExc_RuntimeError,
+                                       "deque mutated during iteration");
+                       return NULL;
+               }
+
+               /* Advance left block/index pair */
+               leftindex++;
+               if (leftindex == BLOCKLEN) {
+                       assert (leftblock->rightlink != NULL);
+                       leftblock = leftblock->rightlink;
+                       leftindex = 0;
+               }
+       }
+       return PyLong_FromSsize_t(count);
+}
+
+PyDoc_STRVAR(count_doc,
+"D.count(value) -> integer -- return number of occurrences of value");
+
 static Py_ssize_t
 deque_len(dequeobject *deque)
 {
@@ -933,6 +973,8 @@ static PyMethodDef deque_methods[] = {
                METH_NOARGS,     clear_doc},
        {"__copy__",            (PyCFunction)deque_copy,
                METH_NOARGS,     copy_doc},
+       {"count",               (PyCFunction)deque_count,
+           METH_O,                     count_doc},
        {"extend",              (PyCFunction)deque_extend,
                METH_O,          extend_doc},
        {"extendleft",          (PyCFunction)deque_extendleft,