[O] Insert a line separator in table results

[Xavier Garrido]

Dear orgers,

I would like to programmatically insert a line separator when generating 
a table result. Below is a minimal working example with =python= src block

#+BEGIN_SRC python
  x = [("label 1", "label 2", "label 3"), ("-", "-", "-")]
  x.append((4, 5, 6))
  x.append((7, 8, 9))
  return (x)
#+END_SRC

#+RESULTS:
| label 1 | label 2 | label 3 |
|       - |       - |       - |
|       4 |       5 |       6 |
|       7 |       8 |       9 |

Is there any possibility to interpret dash as line separator ?

Thanks for your help,
Xavier