Issue 7994: Make object.__format__() raise a PendingDeprecationWarning

if the format string is not empty. Manually merge r79596 and r84772
from 2.x.

Also, apparently test_format() from test_builtin never made it into
3.x. I've added it as well. It tests the basic format()
infrastructure.

1 files changed, 20 insertions, 3 deletions

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 8b74e1e..897374d 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -3315,9 +3315,26 @@ object_format(PyObject *self, PyObject *args)
         return NULL;
 
     self_as_str = PyObject_Str(self);
-    if (self_as_str != NULL)
-        result = PyObject_Format(self_as_str, format_spec);
-
+    if (self_as_str != NULL) {
+        /* Issue 7994: If we're converting to a string, we
+	   should reject format specifications */
+        if (PyUnicode_GET_SIZE(format_spec) > 0) {
+	    if (PyErr_WarnEx(PyExc_PendingDeprecationWarning,
+			     "object.__format__ with a non-empty format "
+			     "string is deprecated", 1) < 0) {
+	      goto done;
+	    }
+	    /* Eventually this will become an error:
+	       PyErr_Format(PyExc_TypeError,
+	       "non-empty format string passed to object.__format__");
+	       goto done;
+	    */
+	}
+
+	result = PyObject_Format(self_as_str, format_spec);
+    }
+
+done:
     Py_XDECREF(self_as_str);
 
     return result;