Document one of the many problems with the buffer object.

diff --git a/Objects/bufferobject.c b/Objects/bufferobject.c
index fe2be735bb3c440ebf32f7adf806eb7ffefc3bfc..561d6c160d974d988c3af2db9716c1855dace517 100644 (file)
--- a/Objects/bufferobject.c
+++ b/Objects/bufferobject.c
@@ -228,10 +228,17 @@ buffer_hash(PyBufferObject *self)
        if ( self->b_hash != -1 )
                return self->b_hash;
 
+       /* XXX potential bugs here, a readonly buffer does not imply that the
+        * underlying memory is immutable.  b_readonly is a necessary but not
+        * sufficient condition for a buffer to be hashable.  Perhaps it would
+        * be better to only allow hashing if the underlying object is known to
+        * be immutable (e.g. PyString_Check() is true).  Another idea would
+        * be to call tp_hash on the underlying object and see if it raises
+        * an error. */
        if ( !self->b_readonly )
        {
-               /* ### use different wording, since this is conditional? */
-               PyErr_SetString(PyExc_TypeError, "unhashable type");
+               PyErr_SetString(PyExc_TypeError,
+                               "writable buffers are not hashable");
                return -1;
        }