even better oop

exercises/oop/oop.ipynb

@@ -1318,7 +1318,13 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "**EXERCISE:** There is another method for getting a string representation of a Python object, called `__repr__`. Read carefully [\\_\\_repr\\_\\_ documentation](https://docs.python.org/3/reference/datamodel.html#object.__repr__) and implement the method.\n",
+    "**EXERCISE:** There is another method for getting a string representation of a Python object, called `__repr__`. Read carefully [\\_\\_repr\\_\\_ documentation](https://docs.python.org/3/reference/datamodel.html#object.__repr__) and implement the method. To try it and see if any difference appear with respect to str, call the standard Python functions `repr` and `str` like this:\n",
+    "\n",
+    "```\n",
+    "c = ComplexNumber(3,5)\n",
+    "print(repr(c))\n",
+    "print(str(c))\n",
+    "```\n",
     "\n",
     "**QUESTION**: Would `3.0 + 5.0i` be a valid Python expression ? Should we return it with `__repr__`? Read again also [\\_\\_str\\_\\_ documentation](https://docs.python.org/3/reference/datamodel.html#object.__str__) \n",
     "\n"