Modified itertools.izip() to match the behavior of __builtin__.zip()

which can now take zero arguments.

Doc/lib/libitertools.tex

@@ -226,10 +226,13 @@ by functions or loops that truncate the stream.
   \begin{verbatim}
      def izip(*iterables):
          iterables = map(iter, iterables)
-         while True:
+         while iterables:
              result = [i.next() for i in iterables]
              yield tuple(result)
   \end{verbatim}
+
+  \versionchanged[When no iterables are specified, returns a zero length
+                  iterator instead of raising a TypeError exception]{2.4}  
 \end{funcdesc}
 
 \begin{funcdesc}{repeat}{object\optional{, times}}

Lib/test/test_itertools.py

@@ -87,7 +87,7 @@ class TestBasicOps(unittest.TestCase):
         self.assertEqual(list(izip('abcdef', range(3))), zip('abcdef', range(3)))
         self.assertEqual(take(3,izip('abcdef', count())), zip('abcdef', range(3)))
         self.assertEqual(list(izip('abcdef')), zip('abcdef'))
-        self.assertRaises(TypeError, izip)
+        self.assertEqual(list(izip()), zip())
         self.assertRaises(TypeError, izip, 3)
         self.assertRaises(TypeError, izip, range(3), 3)
         # Check tuple re-use (implementation detail)
@@ -199,6 +199,8 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(ValueError, dropwhile(errfunc, [(4,5)]).next)
 
     def test_StopIteration(self):
+        self.assertRaises(StopIteration, izip().next)
+
         for f in (chain, cycle, izip):
             self.assertRaises(StopIteration, f([]).next)
             self.assertRaises(StopIteration, f(StopNow()).next)
@@ -540,6 +542,9 @@ True
 >>> no(lambda x: x%2==0, [1, 2, 5, 9])
 False
 
+>>> quantify(lambda x: x%2==0, xrange(99))
+50
+
 >>> list(window('abc'))
 [('a', 'b'), ('b', 'c')]
 

Misc/NEWS

@@ -23,6 +23,9 @@ Extension modules
 Library
 -------
 
+- itertools.izip() with no arguments now returns an empty iterator instead
+  of raising a TypeError exception.
+
 - _strptime.py now has a behind-the-scenes caching mechanism for the most
   recent TimeRE instance used along with the last five unique directive
   patterns.  The overall module was also made more thread-safe.

Modules/itertoolsmodule.c

@@ -1510,12 +1510,6 @@ izip_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 	PyObject *result;
 	int tuplesize = PySequence_Length(args);
 
-	if (tuplesize < 1) {
-		PyErr_SetString(PyExc_TypeError,
-				"izip() requires at least one sequence");
-		return NULL;
-	}
-
 	/* args must be a tuple */
 	assert(PyTuple_Check(args));
 
@@ -1598,6 +1592,8 @@ izip_next(izipobject *lz)
 	PyObject *it;
 	PyObject *item;
 
+	if (tuplesize == 0)
+		return NULL;
 	if (result->ob_refcnt == 1) {
 		for (i=0 ; i < tuplesize ; i++) {
 			it = PyTuple_GET_ITEM(lz->ittuple, i);