Fix test in Object-Oriented Example 4 (#262)

* Add __eq__ validation in Example 4
* Add a comment to explain the rationale behind __closure__ testing

---------
Co-authored-by: edoardob90 <edoardob90@gmail.com>

Author: despadam

object_oriented_programming.ipynb

@@ -19,7 +19,7 @@
     "    - [Example 1](#Example-1)\n",
     "  - [Properties and methods](#Properties-and-methods)\n",
     "    - [Example 2](#Example-2)\n",
-    "  - [Python's *special methods*](#Python's-*special-methods*)\n",
+    "  - [Python's special methods](#Python's-special-methods)\n",
     "    - [`__str__` and `__repr__`](#__str__-and-__repr__)\n",
     "      - [Example 3](#Example-3)\n",
     "    - [Comparison methods](#Comparison-methods)\n",
@@ -220,7 +220,7 @@
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   },
   {
@@ -357,7 +357,7 @@
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   },
   {
@@ -367,7 +367,7 @@
     "tags": []
    },
    "source": [
-    "# Python's *special methods*"
+    "# Python's special methods"
    ]
   },
   {
@@ -684,7 +684,7 @@
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   },
   {
@@ -974,7 +974,7 @@
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   },
   {
@@ -1429,7 +1429,7 @@
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   },
   {
@@ -1476,11 +1476,11 @@
     "    Args:\n",
     "        flavors: all available ice cream flavors\n",
     "    Returns:\n",
-    "        - a bowl\n",
+    "        - a Bowl instance\n",
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   },
   {
@@ -1538,7 +1538,7 @@
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   },
   {
@@ -1680,7 +1680,7 @@
     "    \"\"\"\n",
     "\n",
     "    # Write your solution here\n",
-    "    pass"
+    "    return"
    ]
   }
  ],
@@ -1700,7 +1700,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.15"
+   "version": "3.10.13"
   }
  },
  "nbformat": 4,

tutorial/tests/test_object_oriented_programming.py

@@ -13,6 +13,17 @@ def __init__(self):
 # Example 1: Person
 #
 
+# NOTE:
+# When testing the classes returned by the solutions function in the Examples 1-4
+# we often need to check if a class method is implemented and it's using the right attributes.
+# One way to check both is to check if the class's method has the __closure__ attribute.
+# Why?
+#   1. If __method__ is not implemented, Python will fetch object.__method__ instead, which obviously is not a closure
+#       `hasattr(solution_result.__method__, "__closure__")` will return False.
+#   2. If __method__ is implemented, but it's not using the class attributes, it will be a closure
+#       `solution_result.__method__.__closure__ is None` will return False.
+# Reference: https://github.com/empa-scientific-it/python-tutorial/pull/249#discussion_r1836867387
+
 
 def reference_oop_person(first_name: str, last_name: str):
     class Person:
@@ -211,6 +222,9 @@ def validate_oop_compare_persons(solution_result):
     assert (
         type(solution_result).__name__ == "Person"
     ), "The class should be named 'Person'."
+    assert hasattr(
+        solution_result.__eq__, "__closure__"
+    ), "Make sure that the class is properly implementing the __eq__() method."
     # Check the class attributes
     try:
         attrs = list(vars(solution_result))