Further encapsulation example

Author: tomasff

week5/w5.ipynb

@@ -317,7 +317,60 @@
    "source": [
     "We can now represent a person with attributes name, age, and profession. We can introduce a person, and a person can eat.\n",
     "This brings us to one of the core principles associated with OOP, **encapsulation**: the object's methods and attributes\n",
-    "are bundled as a single-unit. We also **abstract** away the implementation details of each method. As a programmer you can invoke `eat`\n",
+    "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",
+    "expose what is absolutely necessary to the \"outside world\"."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Not enough energy!\n",
+      "Walking...\n"
+     ]
+    }
+   ],
+   "source": [
+    "class Person:\n",
+    "    def __init__(self, name, age, profession):\n",
+    "        self.name = name\n",
+    "        self.age = age\n",
+    "        self.profession = profession\n",
+    "        self._energy = 0\n",
+    "\n",
+    "    def introduce(self):\n",
+    "        print(f\"I'm {self.name}, {self.age} years old. I'm a {self.profession}.\")\n",
+    "    \n",
+    "    def eat(self, food):\n",
+    "        self._energy += 9\n",
+    "        return \"\"\n",
+    "\n",
+    "    def walk(self):\n",
+    "        if self._energy < 10:\n",
+    "            print(\"Not enough energy!\")\n",
+    "        else:\n",
+    "            print(\"Walking...\")\n",
+    "\n",
+    "my_person = Person(\"donald knuth\", 84, \"computer scientist\")\n",
+    "my_person.eat(\"food\")\n",
+    "my_person.walk()\n",
+    "my_person.eat(\"food\")\n",
+    "my_person.walk()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "We also **abstracted** the implementation details of each method. As a programmer you can invoke `eat`\n",
     "or `introduce` without having to worry about what's going on in the background."
    ]
   },
@@ -463,6 +516,11 @@
     "the behaviour of the method, in which case you don't need to invoke the method from the parent class."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": []
+  },
   {
    "cell_type": "markdown",
    "metadata": {},