Patch #1686487: you can now pass any mapping after '**' in function calls.

Doc/ref/ref5.tex

@@ -704,7 +704,7 @@ It is unusual for both keyword arguments and the
 this confusion does not arise.
 
 If the syntax \samp{**expression} appears in the function call,
-\samp{expression} must evaluate to a (subclass of) dictionary, the
+\samp{expression} must evaluate to a mapping, the
 contents of which are treated as additional keyword arguments.  In the
 case of a keyword appearing in both \samp{expression} and as an
 explicit keyword argument, a \exception{TypeError} exception is

Lib/test/output/test_extcall

@@ -9,6 +9,9 @@ test_extcall
 (1, 2, 3) {'a': 4, 'b': 5}
 (1, 2, 3, 4, 5) {'a': 6, 'b': 7}
 (1, 2, 3, 6, 7) {'a': 8, 'b': 9, 'x': 4, 'y': 5}
+(1, 2, 3) {'a': 4, 'b': 5}
+(1, 2, 3, 4, 5) {'a': 6, 'b': 7}
+(1, 2, 3, 6, 7) {'a': 8, 'b': 9, 'x': 4, 'y': 5}
 TypeError: g() takes at least 1 argument (0 given)
 TypeError: g() takes at least 1 argument (0 given)
 TypeError: g() takes at least 1 argument (0 given)
@@ -25,12 +28,12 @@ g() got multiple values for keyword argument 'x'
 g() got multiple values for keyword argument 'b'
 f() keywords must be strings
 h() got an unexpected keyword argument 'e'
-h() argument after * must be a sequence
-dir() argument after * must be a sequence
-NoneType object argument after * must be a sequence
-h() argument after ** must be a dictionary
-dir() argument after ** must be a dictionary
-NoneType object argument after ** must be a dictionary
+h() argument after * must be a sequence, not function
+dir() argument after * must be a sequence, not function
+NoneType object argument after * must be a sequence, not function
+h() argument after ** must be a mapping, not function
+dir() argument after ** must be a mapping, not function
+NoneType object argument after ** must be a mapping, not function
 dir() got multiple values for keyword argument 'b'
 3 512 True
 3

Lib/test/test_extcall.py

 from test.test_support import verify, verbose, TestFailed, sortdict
 from UserList import UserList
+from UserDict import UserDict
 
 def e(a, b):
     print a, b
@@ -25,6 +26,12 @@ f(1, 2, 3, **{'a':4, 'b':5})
 f(1, 2, 3, *(4, 5), **{'a':6, 'b':7})
 f(1, 2, 3, x=4, y=5, *(6, 7), **{'a':8, 'b':9})
 
+
+f(1, 2, 3, **UserDict(a=4, b=5))
+f(1, 2, 3, *(4, 5), **UserDict(a=6, b=7))
+f(1, 2, 3, x=4, y=5, *(6, 7), **UserDict(a=8, b=9))
+
+
 # Verify clearing of SF bug #733667
 try:
     e(c=3)

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.6 alpha 1?
 Core and builtins
 -----------------
 
+- Patch #1686487: you can now pass any mapping after '**' in function
+  calls.
+
 - except clauses may now be spelled either "except E, target:" or
   "except E as target:". This is to provide forwards compatibility with
   Python 3.0.

Python/ceval.c

@@ -3790,13 +3790,31 @@ ext_do_call(PyObject *func, PyObject ***pp_stack, int flags, int na, int nk)
 
 	if (flags & CALL_FLAG_KW) {
 		kwdict = EXT_POP(*pp_stack);
-		if (!(kwdict && PyDict_Check(kwdict))) {
-			PyErr_Format(PyExc_TypeError,
-				     "%s%s argument after ** "
-				     "must be a dictionary",
-				     PyEval_GetFuncName(func),
-				     PyEval_GetFuncDesc(func));
-			goto ext_call_fail;
+		if (!PyDict_Check(kwdict)) {
+			PyObject *d;
+			d = PyDict_New();
+			if (d == NULL)
+				goto ext_call_fail;
+			if (PyDict_Update(d, kwdict) != 0) {
+				Py_DECREF(d);
+				/* PyDict_Update raises attribute
+				 * error (percolated from an attempt
+				 * to get 'keys' attribute) instead of
+				 * a type error if its second argument
+				 * is not a mapping.
+				 */
+				if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+					PyErr_Format(PyExc_TypeError,
+						     "%.200s%.200s argument after ** "
+						     "must be a mapping, not %.200s",
+						     PyEval_GetFuncName(func),
+						     PyEval_GetFuncDesc(func),
+						     kwdict->ob_type->tp_name);
+				}
+				goto ext_call_fail;
+			}
+			Py_DECREF(kwdict);
+			kwdict = d;
 		}
 	}
 	if (flags & CALL_FLAG_VAR) {
@@ -3807,10 +3825,11 @@ ext_do_call(PyObject *func, PyObject ***pp_stack, int flags, int na, int nk)
 			if (t == NULL) {
 				if (PyErr_ExceptionMatches(PyExc_TypeError)) {
 					PyErr_Format(PyExc_TypeError,
-						     "%s%s argument after * "
-						     "must be a sequence",
+						     "%.200s%.200s argument after * "
+						     "must be a sequence, not %200s",
 						     PyEval_GetFuncName(func),
-						     PyEval_GetFuncDesc(func));
+						     PyEval_GetFuncDesc(func),
+						     stararg->ob_type->tp_name);
 				}
 				goto ext_call_fail;
 			}