W5: Person constructor

Author: tomasff

week5/w5.ipynb

@@ -169,7 +169,81 @@
   {
    "cell_type": "markdown",
    "metadata": {},
-   "source": []
+   "source": [
+    "We can now create an *instance* of Person with the same notation used to call functions!\n",
+    "`my_person` is an instance of `Person`."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "my_person = Person()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Great, we've defined a Person class, but this doesn't really do much right now.\n",
+    "What characteristics might we want to store about a person? These will determine what the attributes our objects will have.\n",
+    "To keep things simple, let's consider a person's name, age, and profession.\n",
+    "\n",
+    "We need to update our \"blueprint\", the `Person` class, so that instances of this class contain these attributes!\n",
+    "This is done using a constructor. The constructor is a special method used to define how instances of the `Person` class\n",
+    "should be initialized. When we instantiate a new instance of `Person` with `my_person = Person()`, Python will attempt to invoke\n",
+    "a method called `__init__` if it exists.\n",
+    "\n",
+    "In order to define a constructor, we define a method, more precisely an instance method, with the name `__init__`\n",
+    "in our class (**important:** note the indentation of the method).\n",
+    "\n",
+    "Instance methods are \"attached\" to an object and they can refer to other methods and attributes of the object.\n",
+    "To that end, we need to be able to refer to the object which owns the instance method.\n",
+    "This is done by adding a `self` parameter to **every** instance method. This parameter **must** also be the first\n",
+    "parameter of every instance method.\n",
+    "\n",
+    "Below we have added a constructor to the `Person` class. It takes `self` (the object which was just created), the name of the\n",
+    "person, age, and profession as parameters and then we \"store\" these in the new object. We can access and set the attributes\n",
+    "of an object using a `.` followed by the attribute name as shown below.\n",
+    "\n",
+    "You may have also noticed that this method starts and ends with `__`. \n",
+    "There are other methods named in a similar way.\n",
+    "These methods are often called *magic methods* and used to defined very specific behaviours (If you're curious you can find out more [here](https://docs.python.org/3/reference/datamodel.html#special-method-names))."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "class Person:\n",
+    "    def __init__(self, name, age, profession):\n",
+    "        self.name = name\n",
+    "        self.age = age\n",
+    "        self.profession = profession"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Now we can instantiate a person like so."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "my_person = Person(\"tomas\", 20, \"computer scientist\")\n",
+    "\n",
+    "print(my_person.name)\n",
+    "print(my_person.age)"
+   ]
   },
   {
    "cell_type": "markdown",