Issue #4806: Avoid masking original TypeError in call with * unpacking

Based on patch by Hagen Fürstenau and Daniel Urban.

Lib/test/test_extcall.py

@@ -114,7 +114,7 @@ Verify clearing of SF bug #733667
     >>> g(*Nothing())
     Traceback (most recent call last):
       ...
-    TypeError: g() argument after * must be a sequence, not Nothing
+    TypeError: g() argument after * must be an iterable, not Nothing
 
     >>> class Nothing:
     ...     def __len__(self): return 5
@@ -123,7 +123,7 @@ Verify clearing of SF bug #733667
     >>> g(*Nothing())
     Traceback (most recent call last):
       ...
-    TypeError: g() argument after * must be a sequence, not Nothing
+    TypeError: g() argument after * must be an iterable, not Nothing
 
     >>> class Nothing():
     ...     def __len__(self): return 5
@@ -149,6 +149,45 @@ Verify clearing of SF bug #733667
     >>> g(*Nothing())
     0 (1, 2, 3) {}
 
+Check for issue #4806: Does a TypeError in a generator get propagated with the
+right error message? (Also check with other iterables.)
+
+    >>> def broken(): raise TypeError("myerror")
+    ...
+
+    >>> g(*(broken() for i in range(1)))
+    Traceback (most recent call last):
+      ...
+    TypeError: myerror
+
+    >>> class BrokenIterable1:
+    ...     def __iter__(self):
+    ...         raise TypeError('myerror')
+    ...
+    >>> g(*BrokenIterable1())
+    Traceback (most recent call last):
+      ...
+    TypeError: myerror
+
+    >>> class BrokenIterable2:
+    ...     def __iter__(self):
+    ...         yield 0
+    ...         raise TypeError('myerror')
+    ...
+    >>> g(*BrokenIterable2())
+    Traceback (most recent call last):
+      ...
+    TypeError: myerror
+
+    >>> class BrokenSequence:
+    ...     def __getitem__(self, idx):
+    ...         raise TypeError('myerror')
+    ...
+    >>> g(*BrokenSequence())
+    Traceback (most recent call last):
+      ...
+    TypeError: myerror
+
 Make sure that the function doesn't stomp the dictionary
 
     >>> d = {'a': 1, 'b': 2, 'c': 3}
@@ -188,17 +227,17 @@ What about willful misconduct?
     >>> h(*h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after * must be a sequence, not function
+    TypeError: h() argument after * must be an iterable, not function
 
     >>> dir(*h)
     Traceback (most recent call last):
       ...
-    TypeError: dir() argument after * must be a sequence, not function
+    TypeError: dir() argument after * must be an iterable, not function
 
     >>> None(*h)
     Traceback (most recent call last):
       ...
-    TypeError: NoneType object argument after * must be a sequence, \
+    TypeError: NoneType object argument after * must be an iterable, \
 not function
 
     >>> h(**h)

Misc/NEWS

@@ -10,6 +10,10 @@ Release date: tba
 Core and Builtins
 -----------------
 
+- Issue #4806: Avoid masking the original TypeError exception when using star
+  (*) unpacking in function calls.  Based on patch by Hagen Fürstenau and
+  Daniel Urban.
+
 - Issue #26154: Add a new private _PyThreadState_UncheckedGet() function to get
   the current Python thread state, but don't issue a fatal error if it is NULL.
   This new function must be used instead of accessing directly the

Python/ceval.c

@@ -4935,16 +4935,18 @@ ext_do_call(PyObject *func, PyObject ***pp_stack, int flags, int na, int nk)
         stararg = EXT_POP(*pp_stack);
         if (!PyTuple_Check(stararg)) {
             PyObject *t = NULL;
+            if (Py_TYPE(stararg)->tp_iter == NULL &&
+                    !PySequence_Check(stararg)) {
+                PyErr_Format(PyExc_TypeError,
+                             "%.200s%.200s argument after * "
+                             "must be an iterable, not %.200s",
+                             PyEval_GetFuncName(func),
+                             PyEval_GetFuncDesc(func),
+                             stararg->ob_type->tp_name);
+                goto ext_call_fail;
+            }
             t = PySequence_Tuple(stararg);
             if (t == NULL) {
-                if (PyErr_ExceptionMatches(PyExc_TypeError)) {
-                    PyErr_Format(PyExc_TypeError,
-                                 "%.200s%.200s argument after * "
-                                 "must be a sequence, not %.200s",
-                                 PyEval_GetFuncName(func),
-                                 PyEval_GetFuncDesc(func),
-                                 stararg->ob_type->tp_name);
-                }
                 goto ext_call_fail;
             }
             Py_DECREF(stararg);