Add polymorphism example

Author: tomasff

week5/w5.ipynb

@@ -320,24 +320,15 @@
     "are bundled as a single-unit.\n",
     "\n",
     "As a further example, for **encapsulation**, our class can have other attributes that are not exposed to the \"outside world\".\n",
-    "For example, we can keep track of the energy of a Person using `_energy` (note the underscore, this represents a private attribute, that is, it shouldn't be used anywhere outside the class), and we use this to decide whether or not a person can walk. The key takeaway for encapsulation is that we only\n",
+    "For example, we can keep track of the energy of a Person using `_energy` (note the underscore, this represents a protected attribute, that is, it shouldn't be used anywhere outside the class), and we use this to decide whether or not a person can walk. The key takeaway for encapsulation is that we only\n",
     "expose what is absolutely necessary to the \"outside world\"."
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": null,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "Not enough energy!\n",
-      "Walking...\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "class Person:\n",
     "    def __init__(self, name, age, profession):\n",
@@ -519,7 +510,68 @@
   {
    "cell_type": "markdown",
    "metadata": {},
-   "source": []
+   "source": [
+    "Finally, suppose we want to change the introduction of each profession. We can override the `introduce` method for `Doctor` and `Profession`.\n",
+    "Then, if we have a group of people, for example, a list of instances of `Person`, we can call `introduce` and the correct introduction will be used!\n",
+    "This is called **polymorphism**: the same code can be used with slightly different objects and behave in a different way."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "I'm a computer scientist!!!111!!\n",
+      "I'm Person, 25 years old. I'm a phd.\n",
+      "I'm Person2, 30 years old. I'm a mechanic.\n",
+      "I'm a doctor!!!111!!\n"
+     ]
+    }
+   ],
+   "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",
+    "    def introduce(self):\n",
+    "        print(\"I'm a computer scientist!!!111!!\")\n",
+    "    \n",
+    "class Doctor(Person):\n",
+    "    def __init__(self, name, age):\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",
+    "    def introduce(self):\n",
+    "        print(\"I'm a doctor!!!111!!\")\n",
+    "\n",
+    "\n",
+    "donald_knuth = ComputerScientist(\"donald knuth\", 84)\n",
+    "person = Person(\"Person\", 25, \"phd\")\n",
+    "person_2 = Person(\"Person2\", 30, \"mechanic\")\n",
+    "doctor = Doctor(\"John Doe\", 65)\n",
+    "\n",
+    "people = [donald_knuth, person, person_2, doctor]\n",
+    "\n",
+    "for p in people:\n",
+    "    p.introduce()"
+   ]
   },
   {
    "cell_type": "markdown",