diff -r 95fb7b66107e Include/compile.h
--- a/Include/compile.h	Fri Mar 22 00:06:20 2013 +0100
+++ b/Include/compile.h	Fri Mar 22 01:52:02 2013 +0100
@@ -53,4 +53,6 @@ PyAPI_FUNC(PyObject*) _Py_Mangle(PyObjec
 #define Py_file_input 257
 #define Py_eval_input 258
 
+PyAPI_DATA(PyObject*) Py_ASTHook;
+
 #endif /* !Py_COMPILE_H */
diff -r 95fb7b66107e Python/compile.c
--- a/Python/compile.c	Fri Mar 22 00:06:20 2013 +0100
+++ b/Python/compile.c	Fri Mar 22 01:52:02 2013 +0100
@@ -42,6 +42,8 @@ int Py_OptimizeFlag = 0;
 #define COMP_SETCOMP  2
 #define COMP_DICTCOMP 3
 
+PyObject *Py_ASTHook = NULL;
+
 struct instr {
     unsigned i_jabs : 1;
     unsigned i_jrel : 1;
@@ -3860,7 +3862,9 @@ assemble_lnotab(struct assembler *a, str
     d_lineno = i->i_lineno - a->a_lineno;
 
     assert(d_bytecode >= 0);
+#if 0
     assert(d_lineno >= 0);
+#endif
 
     if(d_bytecode == 0 && d_lineno == 0)
         return 1;
diff -r 95fb7b66107e Python/pythonrun.c
--- a/Python/pythonrun.c	Fri Mar 22 00:06:20 2013 +0100
+++ b/Python/pythonrun.c	Fri Mar 22 01:52:02 2013 +0100
@@ -2072,6 +2072,56 @@ Py_SymtableString(const char *str, const
     return st;
 }
 
+static mod_ty
+call_ast_hook(mod_ty mod, PyArena *arena, const char *filename, int start)
+{
+    PyObject *ast, *fileobj, *res;
+    int mode;
+
+    if (!Py_ASTHook)
+        return mod;
+
+    if (start == Py_file_input)
+        mode = 0; /* exec */
+    else if (start == Py_eval_input)
+        mode = 1; /* eval */
+    else {
+        assert(start == Py_single_input);
+        mode = 2; /* single */
+    }
+
+    ast = PyAST_mod2obj(mod);
+    if (ast == NULL)
+        return NULL;
+
+    if (filename != NULL) {
+        fileobj = PyUnicode_DecodeFSDefault(filename);
+        if (fileobj == NULL) {
+            Py_DECREF(ast);
+            return NULL;
+        }
+    }
+    else {
+        Py_INCREF(Py_None);
+        fileobj = Py_None;
+    }
+
+    res = PyObject_CallFunction(Py_ASTHook, "OO", ast, fileobj);
+    Py_DECREF(ast);
+    Py_DECREF(fileobj);
+    if (res == NULL)
+        return NULL;
+
+    mod = PyAST_obj2mod(res, arena, mode);
+    Py_DECREF(ast);
+    if (mod == NULL)
+        return NULL;
+    if (!PyAST_Validate(mod))
+        return NULL;
+
+    return mod;
+}
+
 /* Preferred access to parser is through AST. */
 mod_ty
 PyParser_ASTFromString(const char *s, const char *filename, int start,
@@ -2099,7 +2149,10 @@ PyParser_ASTFromString(const char *s, co
         mod = NULL;
     }
     err_free(&err);
-    return mod;
+    if (mod == NULL)
+        return NULL;
+
+    return call_ast_hook(mod, arena, filename, start);
 }
 
 mod_ty
@@ -2132,7 +2185,10 @@ PyParser_ASTFromFile(FILE *fp, const cha
         mod = NULL;
     }
     err_free(&err);
-    return mod;
+    if (mod == NULL)
+        return NULL;
+
+    return call_ast_hook(mod, arena, filename, start);
 }
 
 /* Simplified interface to parsefile -- return node or set exception */
diff -r 95fb7b66107e Python/sysmodule.c
--- a/Python/sysmodule.c	Fri Mar 22 00:06:20 2013 +0100
+++ b/Python/sysmodule.c	Fri Mar 22 01:52:02 2013 +0100
@@ -1056,6 +1056,30 @@ PyDoc_STRVAR(sys_clear_type_cache__doc__
 "_clear_type_cache() -> None\n\
 Clear the internal type lookup cache.");
 
+static PyObject *
+sys_setasthook(PyObject *self, PyObject *hook)
+{
+    if (!PyCallable_Check(hook)) {
+        PyErr_SetString(PyExc_TypeError, "the argument must be callable");
+        return NULL;
+    }
+
+    Py_XDECREF(Py_ASTHook);
+    Py_INCREF(hook);
+    Py_ASTHook = hook;
+
+
+
+    Py_INCREF(Py_None);
+    return Py_None;
+}
+
+PyDoc_STRVAR(setasthook_doc,
+"setasthook(function)\n\
+\n\
+Set an hook on the AST compiler."
+);
+
 
 static PyMethodDef sys_methods[] = {
     /* Might as well keep this in alphabetic order */
@@ -1128,6 +1152,7 @@ static PyMethodDef sys_methods[] = {
 #endif
     {"settrace",        sys_settrace, METH_O, settrace_doc},
     {"gettrace",        sys_gettrace, METH_NOARGS, gettrace_doc},
+    {"setasthook",      sys_setasthook, METH_O, setasthook_doc},
     {"call_tracing", sys_call_tracing, METH_VARARGS, call_tracing_doc},
     {"_debugmallocstats", sys_debugmallocstats, METH_VARARGS,
      debugmallocstats_doc},