update __doc__ for function object

Author: xuantengh

Objects/funcobject.c

@@ -162,7 +162,7 @@ PyFunction_NewWithQualName(PyObject *code, PyObject *globals, PyObject *qualname
     PyObject *consts = code_obj->co_consts;
     assert(PyTuple_Check(consts));
     PyObject *doc;
-    if (PyTuple_Size(consts) >= 1) {
+    if (PyTuple_Size(consts) >= 1 && code_obj->co_flags & CO_HAS_DOCSTRING) {
         doc = PyTuple_GetItem(consts, 0);
         if (!PyUnicode_Check(doc)) {
             doc = Py_None;

Python/codegen.c

@@ -772,7 +772,6 @@ _PyCodegen_Body(compiler *c, location loc, asdl_stmt_seq *stmts, bool is_interac
             assert(st->kind == Expr_kind);
             location loc = LOC(st->v.Expr.value);
             ADDOP_LOAD_CONST(c, loc, cleandoc);
-
             Py_DECREF(cleandoc);
             RETURN_IF_ERROR(codegen_nameop(c, NO_LOCATION, &_Py_ID(__doc__), Store));
         }