bpo-30399: Get rid of trailing comma in the repr of BaseException.

Lib/test/test_baseexception.py

@@ -92,7 +92,7 @@ def test_interface_single_arg(self):
         exc = Exception(arg)
         results = ([len(exc.args), 1], [exc.args[0], arg],
                    [str(exc), str(arg)],
-            [repr(exc), exc.__class__.__name__ + repr(exc.args)])
+            [repr(exc), '%s(%r)' % (exc.__class__.__name__, arg)])
         self.interface_test_driver(results)
 
     def test_interface_multi_arg(self):

Lib/test/test_httplib.py

@@ -497,7 +497,7 @@ def test_status_lines(self):
 
     def test_bad_status_repr(self):
         exc = client.BadStatusLine('')
-        self.assertEqual(repr(exc), '''BadStatusLine("\'\'",)''')
+        self.assertEqual(repr(exc), '''BadStatusLine("''")''')
 
     def test_partial_reads(self):
         # if we have Content-Length, HTTPResponse knows when to close itself,

Lib/test/test_yield_from.py

@@ -418,7 +418,7 @@ def g2(v = None):
             "Yielded g2 spam",
             "Yielded g2 more spam",
             "Finishing g2",
-            "g2 returned StopIteration(3,)",
+            "g2 returned StopIteration(3)",
             "Yielded g1 eggs",
             "Finishing g1",
         ])
@@ -696,15 +696,15 @@ def g(r):
             "g starting",
             "f resuming g",
             "g returning 1",
-            "f caught StopIteration(1,)",
+            "f caught StopIteration(1)",
             "g starting",
             "f resuming g",
             "g returning (2,)",
-            "f caught StopIteration((2,),)",
+            "f caught StopIteration((2,))",
             "g starting",
             "f resuming g",
-            "g returning StopIteration(3,)",
-            "f caught StopIteration(StopIteration(3,),)",
+            "g returning StopIteration(3)",
+            "f caught StopIteration(StopIteration(3))",
         ])
 
     def test_send_and_return_with_value(self):
@@ -741,17 +741,17 @@ def g(r):
             "f sending spam to g",
             "g received 'spam'",
             "g returning 1",
-            'f caught StopIteration(1,)',
+            'f caught StopIteration(1)',
             'g starting',
             'f sending spam to g',
             "g received 'spam'",
             'g returning (2,)',
-            'f caught StopIteration((2,),)',
+            'f caught StopIteration((2,))',
             'g starting',
             'f sending spam to g',
             "g received 'spam'",
-            'g returning StopIteration(3,)',
-            'f caught StopIteration(StopIteration(3,),)'
+            'g returning StopIteration(3)',
+            'f caught StopIteration(StopIteration(3))'
         ])
 
     def test_catching_exception_from_subgen_and_returning(self):

Misc/NEWS.d/next/Core and Builtins/2017-10-12-22-21-01.bpo-30399.45f1gv.rst

@@ -0,0 +1,2 @@
+Standard repr() of BaseException with a single argument no longer contains
+redundant trailing comma.

Objects/exceptions.c

@@ -117,7 +117,11 @@ static PyObject *
 BaseException_repr(PyBaseExceptionObject *self)
 {
     const char *name = _PyType_Name(Py_TYPE(self));
-    return PyUnicode_FromFormat("%s%R", name, self->args);
+    if (PyTuple_GET_SIZE(self->args) == 1)
+        return PyUnicode_FromFormat("%s(%R)", name,
+                                    PyTuple_GET_ITEM(self->args, 0));
+    else
+        return PyUnicode_FromFormat("%s%R", name, self->args);
 }
 
 /* Pickling support */