Issue #7410: deepcopy of itertools.count was resetting the count.

Lib/test/test_itertools.py

@@ -7,6 +7,8 @@ from fractions import Fraction
 import sys
 import operator
 import random
+import copy
+import pickle
 from functools import reduce
 maxsize = support.MAX_Py_ssize_t
 minsize = -maxsize-1
@@ -352,6 +354,13 @@ class TestBasicOps(unittest.TestCase):
             r2 = 'count(%r)'.__mod__(i).replace('L', '')
             self.assertEqual(r1, r2)
 
+        # check copy, deepcopy, pickle
+        for value in -3, 3, maxsize-5, maxsize+5:
+            c = count(value)
+            self.assertEqual(next(copy.copy(c)), value)
+            self.assertEqual(next(copy.deepcopy(c)), value)
+            self.assertEqual(next(pickle.loads(pickle.dumps(c))), value)
+
     def test_count_with_stride(self):
         self.assertEqual(lzip('abc',count(2,3)), [('a', 2), ('b', 5), ('c', 8)])
         self.assertEqual(lzip('abc',count(start=2,step=3)),

Misc/NEWS

@@ -52,6 +52,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #7410: deepcopy of itertools.count was resetting the count.
+
 - Issue #4486: When an exception has an explicit cause, do not print its
   implicit context too.  This affects the `traceback` module as well as
   built-in exception printing.

Modules/itertoolsmodule.c

@@ -3049,6 +3049,22 @@ count_repr(countobject *lz)
 								lz->long_cnt, lz->long_step);
 }
 
+static PyObject *
+count_reduce(countobject *lz)
+{
+	if (lz->cnt == PY_SSIZE_T_MAX)
+		return Py_BuildValue("O(OO)", Py_TYPE(lz), lz->long_cnt, lz->long_step);
+	return Py_BuildValue("O(n)", Py_TYPE(lz), lz->cnt);
+}
+
+PyDoc_STRVAR(count_reduce_doc, "Return state information for pickling.");
+
+static PyMethodDef count_methods[] = {
+	{"__reduce__",	(PyCFunction)count_reduce,	METH_NOARGS,
+	 count_reduce_doc},
+	{NULL,		NULL}	/* sentinel */
+};
+
 PyDoc_STRVAR(count_doc,
 			 "count(start=0, step=1]) --> count object\n\
 \n\
@@ -3090,7 +3106,7 @@ static PyTypeObject count_type = {
 	0,				/* tp_weaklistoffset */
 	PyObject_SelfIter,		/* tp_iter */
 	(iternextfunc)count_next,	/* tp_iternext */
-	0,				/* tp_methods */
+	count_methods,				/* tp_methods */
 	0,				/* tp_members */
 	0,				/* tp_getset */
 	0,				/* tp_base */