Michael Hudson <mwh21@cam.ac.uk>:

The error message refers to "append", yet the operation in
question is "concat".

Objects/tupleobject.c

@@ -362,7 +362,7 @@ tupleconcat(a, bb)
 	PyTupleObject *np;
 	if (!PyTuple_Check(bb)) {
 		PyErr_Format(PyExc_TypeError,
-       		     "can only append tuple (not \"%.200s\") to tuple",
+       		     "can only concatenate tuple (not \"%.200s\") to tuple",
 			     bb->ob_type->tp_name);
 		return NULL;
 	}