Issue #3602

Python/_warnings.c

 #include "Python.h"
+#include "code.h"  /* For DeprecationWarning about adding 'line'. */
 #include "frameobject.h"
 
 #define MODULE_NAME "_warnings"
 #define DEFAULT_ACTION_NAME "default_action"
 
 PyDoc_STRVAR(warnings__doc__,
 MODULE_NAME " provides basic warning filtering support.\n"
 "It is a helper module to speed up interpreter start-up.");
 
 /* Both 'filters' and 'onceregistry' can be set in warnings.py;
@@ skipping 397 matching lines @@
                                     "warnings.showwarning() must be set to a "
                                     "function or method");
                     Py_DECREF(show_fxn);
                     goto cleanup;
                 }
 
                 defaults = PyFunction_GetDefaults(check_fxn);
                 /* A proper implementation of warnings.showwarning() should
                     have at least two default arguments. */
                 if ((defaults == NULL) || (PyTuple_Size(defaults) < 2)) {
-                    if (PyErr_WarnEx(PyExc_DeprecationWarning, msg, 1) < 0) {
-                        Py_DECREF(show_fxn);
-                        goto cleanup;
+                    PyCodeObject *code = (PyCodeObject *)
+                                                PyFunction_GetCode(check_fxn);
+                    if (!(code->co_flags & CO_VARARGS)) {
+                        if (PyErr_WarnEx(PyExc_DeprecationWarning, msg, 1) <
+                                0) {
+                            Py_DECREF(show_fxn);
+                            goto cleanup;
+                        }
                     }
-                }
+                }
                 res = PyObject_CallFunctionObjArgs(show_fxn, message, category,
                                                     filename, lineno_obj,
                                                     NULL);
                 Py_DECREF(show_fxn);
                 Py_XDECREF(res);
                 if (res == NULL)
                     goto cleanup;
             }
         }
     }
@@ skipping 465 matching lines @@
     Py_INCREF(_once_registry);
     if (PyModule_AddObject(m, "once_registry", _once_registry) < 0)
         return;
 
     default_action = PyString_InternFromString("default");
     if (default_action == NULL)
         return;
     if (PyModule_AddObject(m, DEFAULT_ACTION_NAME, default_action) < 0)
         return;
 }