Make starmap() match its pure python definition and accept any itertable input (not just tuples).

Doc/library/itertools.rst

@@ -330,17 +330,19 @@ loops that truncate the stream.
 
 .. function:: starmap(function, iterable)
 
-   Make an iterator that computes the function using arguments tuples obtained from
+   Make an iterator that computes the function using arguments obtained from
    the iterable.  Used instead of :func:`imap` when argument parameters are already
    grouped in tuples from a single iterable (the data has been "pre-zipped").  The
    difference between :func:`imap` and :func:`starmap` parallels the distinction
    between ``function(a,b)`` and ``function(*c)``. Equivalent to::
 
       def starmap(function, iterable):
-          iterable = iter(iterable)
-          while True:
-              yield function(*iterable.next())
+          for args in iterable:
+              yield function(*args)
 
+   .. versionchanged:: 2.6
+      Previously, :func:`starmap` required the function arguments to be tuples.
+      Now, any iterable is allowed.
 
 .. function:: takewhile(predicate, iterable)
 

Lib/test/test_itertools.py

@@ -292,7 +292,8 @@ class TestBasicOps(unittest.TestCase):
         self.assertEqual(take(3, starmap(operator.pow, izip(count(), count(1)))),
                          [0**1, 1**2, 2**3])
         self.assertEqual(list(starmap(operator.pow, [])), [])
-        self.assertRaises(TypeError, list, starmap(operator.pow, [[4,5]]))
+        self.assertEqual(list(starmap(operator.pow, [iter([4,5])])), [4**5])
+        self.assertRaises(TypeError, list, starmap(operator.pow, [None]))
         self.assertRaises(TypeError, starmap)
         self.assertRaises(TypeError, starmap, operator.pow, [(4,5)], 'extra')
         self.assertRaises(TypeError, starmap(10, [(4,5)]).next)

Misc/NEWS

@@ -993,6 +993,9 @@ Extension Modules
   the context manager protocol.  The _winreg module also gained a new function
   ``ExpandEnvironmentStrings`` to expand REG_EXPAND_SZ keys.
 
+- itertools.starmap() now accepts any iterable input. Previously, it required
+  the function inputs to be tuples.
+
 - Issue #1646: Make socket support TIPC. The socket module now has support
   for TIPC under Linux, see http://tipc.sf.net/ for more information.
 

Modules/itertoolsmodule.c

@@ -1356,10 +1356,11 @@ starmap_next(starmapobject *lz)
 	if (args == NULL)
 		return NULL;
 	if (!PyTuple_CheckExact(args)) {
+		PyObject *newargs = PySequence_Tuple(args);
 		Py_DECREF(args);
-		PyErr_SetString(PyExc_TypeError,
-				"iterator must return a tuple");
-		return NULL;
+		if (newargs == NULL)
+			return NULL;
+		args = newargs;
 	}
 	result = PyObject_Call(lz->func, args, NULL);
 	Py_DECREF(args);