W5: Overriding methods

Author: tomasff

week5/w5.ipynb

@@ -383,40 +383,85 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "010101010000111001 code go brrrrrr\n",
-      "Treating a person...\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "class ComputerScientist(Person):\n",
     "    def __init__(self, name, age):\n",
+    "        \"\"\"\n",
+    "        We're invoking the constructor of Person,\n",
+    "        but we set the profession to be \"computer scientist\"\n",
+    "        \"\"\"\n",
     "        super().__init__(name, age, \"computer scientist\")\n",
     "    \n",
     "    def write_code(self):\n",
     "        print(\"010101010000111001 code go brrrrrr\")\n",
     "    \n",
     "class Doctor(Person):\n",
     "    def __init__(self, name, age):\n",
-    "        super().__init__(name, age, \"computer scientist\")\n",
+    "        \"\"\"\n",
+    "        We're invoking the constructor of Person,\n",
+    "        but we set the profession to be \"doctor\"\n",
+    "        \"\"\"\n",
+    "        super().__init__(name, age, \"doctor\")\n",
     "    \n",
     "    def treat_person(self):\n",
     "        print(\"Treating a person...\")\n",
     "\n",
     "donald_knuth = ComputerScientist(\"donald knuth\", 84)\n",
+    "donald_knuth.introduce()\n",
     "donald_knuth.write_code()\n",
     "\n",
     "doctor = Doctor(\"John Doe\", 65)\n",
+    "doctor.introduce()\n",
     "doctor.treat_person()"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "We define the two classes again with a twist: `Doctor` and `ComputerScientist` now inherit from `Person`.\n",
+    "In Python, we can specify the class(es) from which another class inherits from in parenthesis after the class name.\n",
+    "\n",
+    "```py\n",
+    "# Inherit from a single class\n",
+    "class Base(Parent1):\n",
+    "    pass\n",
+    "\n",
+    "# Inherint from multiple classes\n",
+    "class Base(Parent1, Parent2, ...):\n",
+    "    pass\n",
+    "```\n",
+    "\n",
+    "Further, the `Person` class is said to be the parent class of `Doctor` and `ComputerScientist`.\n",
+    "Conversely, the `Doctor` and `ComputerScientist` classes are child classes of the parent `Person`.\n",
+    "\n",
+    "The child classes will inherit everything from the parent class, and can also *override* any method\n",
+    "from the parent classes. In our example, we want instances of `ComputerScientist` to be initialized with the profession \"computer scientist\"\n",
+    "and instances of `Doctor` \"doctor\", however, we also want to maintain the functionality of the `Person` constructor.\n",
+    "\n",
+    "In order to do this, we can override the constructor by re-defining the `__init__` method, and then we call\n",
+    "the constructor of the *super* class (that is, the parent class). We can refer to the super class using `super()`,\n",
+    "and then we invoke `__init__`: `super().__init__(name, age, \"doctor\")`.\n",
+    "\n",
+    "```py\n",
+    "class Doctor(Person):\n",
+    "    def __init__(self, name, age):\n",
+    "        self.name = name\n",
+    "        self.age = age\n",
+    "        self.profession = \"doctor\"\n",
+    "    \n",
+    "    # ...\n",
+    "```\n",
+    "\n",
+    "The implementation above would also work, however, if there are any changes to the constructor of `Person`, you'd have\n",
+    "to copy this over to the new constructor of `Doctor` and `ComputerScientist`.\n",
+    "By invoking the constructor of the parent class we avoid repetition of code. However, there may be cases where you'd want to completly change\n",
+    "the behaviour of the method, in which case you don't need to invoke the method from the parent class."
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -429,27 +474,13 @@
    "metadata": {},
    "source": [
     "TBD:\n",
-    "- polymorphism/abstraction/encapsulation/inheritance a little bit\n",
+    "- polymorphism/abstraction/encapsulation a little bit\n",
     "- attributes (class and instance atttr)\n",
     "- inheritance example\n",
     "- then intermission on anotations\n",
     "- static and class methods"
    ]
   },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "class ComputerScientist(Person):\n",
-    "    def __init__(self, name, age):\n",
-    "        super().__init__(self, name, age, profession=\"Computer Scientist\")\n",
-    "\n",
-    "    def write_code(self):\n",
-    "        print(\"print('hello world')\")"
-   ]
-  },
   {
    "cell_type": "markdown",
    "metadata": {},