{
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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# [Classes](https://docs.python.org/3/tutorial/classes.html#a-first-look-at-classes)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "source": [
    "class MyFirstClass:\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "\n",
    "    def greet(self):\n",
    "        print('Hello {}!'.format(self.name))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_instance = MyFirstClass('John Doe')\n",
    "print('my_intance: {}'.format(my_instance))\n",
    "print('type: {}'.format(type(my_instance)))\n",
    "print('my_instance.name: {}'.format(my_instance.name))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Methods\n",
    "The functions inside classes are called methods. They are used similarly as functions. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "alice = MyFirstClass(name='Alice')\n",
    "alice.greet()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### `__init__()`\n",
    "`__init__()` is a special method that is used for initialising instances of the class. It's called when you create an instance of the class. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Example:\n",
    "    def __init__(self):\n",
    "        print('Now we are inside __init__')\n",
    "        \n",
    "print('creating instance of Example')\n",
    "example = Example()\n",
    "print('instance created')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`__init__()` is typically used for initialising instance variables of your class. These can be listed as arguments after `self`. To be able to access these instance variables later during your instance's lifetime, you have to save them into `self`. `self` is the first argument of the methods of your class and it's your access to the instance variables and other methods. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Example:\n",
    "    def __init__(self, var1, var2):\n",
    "        self.first_var = var1\n",
    "        self.second_var = var2\n",
    "        \n",
    "    def print_variables(self):\n",
    "        print('{} {}'.format(self.first_var, self.second_var))\n",
    "        \n",
    "e = Example('abc', 123)\n",
    "e.print_variables()\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Class variables vs instance variables\n",
    "Class variables are shared between all the instances of that class whereas instance variables can hold different values between different instances of that class."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Example:\n",
    "    # These are class variables\n",
    "    name = 'Example class'\n",
    "    description = 'Just an example of a simple class'\n",
    "\n",
    "    def __init__(self, var1):\n",
    "        # This is an instance variable\n",
    "        self.instance_variable = var1\n",
    "\n",
    "    def show_info(self):\n",
    "        info = 'instance_variable: {}, name: {}, description: {}'.format(\n",
    "            self.instance_variable, Example.name, Example.description)\n",
    "        print(info)\n",
    "\n",
    "\n",
    "inst1 = Example('foo')\n",
    "inst2 = Example('bar')\n",
    "\n",
    "# name and description have identical values between instances\n",
    "assert inst1.name == inst2.name == Example.name\n",
    "assert inst1.description == inst2.description == Example.description\n",
    "\n",
    "# If you change the value of a class variable, it's changed across all instances\n",
    "Example.name = 'Modified name'\n",
    "inst1.show_info()\n",
    "inst2.show_info()"
   ]
  }
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