Index: Python/ast.c
===================================================================
--- Python/ast.c	(revision 53285)
+++ Python/ast.c	(working copy)
@@ -19,6 +19,7 @@
 struct compiling {
     char *c_encoding; /* source encoding */
     PyArena *c_arena; /* arena for allocating memeory */
+    const char *c_filename; /* filename being compiled */
 };
 
 static asdl_seq *seq_for_testlist(struct compiling *, const node *);
@@ -109,6 +110,21 @@
     PyErr_Restore(type, value, tback);
 }
 
+static int
+ast_warn(const node *n, char *msg, const char *filename)
+{
+    if (PyErr_WarnExplicit(PyExc_SyntaxWarning, msg, filename,
+                           LINENO(n), NULL, NULL) < 0) {
+        if (PyErr_ExceptionMatches(PyExc_SyntaxWarning)) {
+            PyErr_SetString(PyExc_SyntaxError, msg);
+            PyErr_SyntaxLocation(filename, LINENO(n));
+        }
+        return 0;
+    }
+    return 1;
+}
+
+
 /* num_stmts() returns number of contained statements.
 
    Use this routine to determine how big a sequence is needed for
@@ -196,6 +212,7 @@
         c.c_encoding = NULL;
     }
     c.c_arena = arena;
+    c.c_filename = filename;
 
     k = 0;
     switch (TYPE(n)) {
@@ -1307,6 +1324,9 @@
         return Dict(keys, values, LINENO(n), n->n_col_offset, c->c_arena);
     }
     case BACKQUOTE: { /* repr */
+        if (!ast_warn(n, "use repr() rather than ``", c->c_filename)) {
+            return NULL;
+        }
         expr_ty expression = ast_for_testlist(c, CHILD(n, 1));
         if (!expression)
             return NULL;