{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "# The smell of classes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "## The \"data bundle\" smell"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:05:51.531289Z",
     "start_time": "2018-07-27T17:05:51.526519+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [],
   "source": [
    "def momentum(mass, velocity):\n",
    "    return mass * velocity\n",
    "\n",
    "def energy(mass, velocity):\n",
    "    return 0.5 * mass * velocity ** 2\n",
    "\n",
    "def update_position(velocity, position, dt):\n",
    "    return position + velocity * dt"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:05:51.905235Z",
     "start_time": "2018-07-27T17:05:51.900153+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n",
      "1.2000000000000002\n",
      "1.0\n"
     ]
    }
   ],
   "source": [
    "# Naive\n",
    "mass1 = 10.0\n",
    "velocity1 = 0.9\n",
    "\n",
    "mass2 = 12.0\n",
    "velocity2 = 0.1\n",
    "\n",
    "print(momentum(mass1, velocity1))\n",
    "print(momentum(mass2, velocity2))\n",
    "print(momentum(mass1, velocity2))  # ??"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "We have two parameters that will be sent to these functions over and over again: `mass` and `velocity`.\n",
    "\n",
    "Moreover, the parameters cannot be mixed up (e.g. the velocity of one particle with the mass of another)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:05:52.116795Z",
     "start_time": "2018-07-27T17:05:52.112569+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n",
      "1.2000000000000002\n"
     ]
    }
   ],
   "source": [
    "masses = [10.0, 12.0]\n",
    "velocities = [0.9, 0.1]\n",
    "\n",
    "print(momentum(masses[0], velocities[0]))\n",
    "print(momentum(masses[1], velocities[1]))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:05:52.548364Z",
     "start_time": "2018-07-27T17:05:52.544726+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n",
      "1.2000000000000002\n"
     ]
    }
   ],
   "source": [
    "particle1 = {'mass': 10.0, 'velocity': 0.9}\n",
    "particle2 = {'mass': 12.0, 'velocity': 0.1}\n",
    "\n",
    "print(momentum(particle1['mass'], particle1['velocity']))\n",
    "print(momentum(particle2['mass'], particle2['velocity']))\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "All of the functions above can be rewritten as a function of this particle \"instance\", eliminating the bookkeeping for the individual parameters."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:05:53.571400Z",
     "start_time": "2018-07-27T17:05:53.567192+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n",
      "1.2000000000000002\n"
     ]
    }
   ],
   "source": [
    "def momentum(particle):\n",
    "    return particle['mass'] * particle['velocity']\n",
    "\n",
    "print(momentum(particle1))\n",
    "print(momentum(particle2))\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "An annoying thing of this solution is that we have to remember the name of the keys in the dictionary, and the solution is sensitive to typos.\n",
    "\n",
    "To solve this, we could write a function to build a particle, a.k.a a \"constructor\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:06:20.004037Z",
     "start_time": "2018-07-27T17:06:19.998500+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n",
      "1.2000000000000002\n"
     ]
    }
   ],
   "source": [
    "def init_particle(mass, velocity):\n",
    "    self = {\n",
    "        'mass': mass,\n",
    "        'velocity': velocity\n",
    "    }\n",
    "    return self\n",
    "\n",
    "particle1 = init_particle(10.0, 0.9)\n",
    "particle2 = init_particle(12.0, 0.1)\n",
    "print(momentum(particle1))\n",
    "print(momentum(particle2))\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "`particle1` and `particle2` are called \"instances\" of the particle \"class\".\n",
    "\n",
    "Python classes are a way to formalize this pattern: creating a bundle of data that belongs together. E.g. the parameters of an experiment, the results of a simulation, etc."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "## Introducing classes as a data bundle template"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-08-04T13:04:49.208543Z",
     "start_time": "2018-08-04T15:04:49.203180+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [],
   "source": [
    "class Particle:\n",
    "    def __init__(self, mass, velocity):\n",
    "        self.mass = mass\n",
    "        self.velocity = velocity\n",
    "\n",
    "particle1 = Particle(10.0, 0.9)\n",
    "particle2 = Particle(12.0, 0.1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:07:09.818544Z",
     "start_time": "2018-07-27T17:07:09.814535+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "0.9"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "particle1.velocity"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:07:09.997264Z",
     "start_time": "2018-07-27T17:07:09.994114+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "12.0"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "particle2.mass"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T15:07:11.559629Z",
     "start_time": "2018-07-27T17:07:11.555632+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    },
    "scrolled": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'mass': 10.0, 'velocity': 0.9}"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "particle1.__dict__"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "## Class methods"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-07-27T12:13:56.972938Z",
     "start_time": "2018-07-27T14:13:56.969323+02:00"
    },
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n",
      "1.2000000000000002\n"
     ]
    }
   ],
   "source": [
    "def momentum(particle):\n",
    "    return particle.mass * particle.velocity\n",
    "\n",
    "print(momentum(particle1))\n",
    "print(momentum(particle2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n"
     ]
    }
   ],
   "source": [
    "class Particle:\n",
    "    def __init__(self, mass, velocity):\n",
    "        self.mass = mass\n",
    "        self.velocity = velocity\n",
    "\n",
    "    def momentum(self):\n",
    "        return self.mass * self.velocity\n",
    "\n",
    "particle1 = Particle(10.0, 0.9)\n",
    "print(particle1.momentum())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "pycharm": {
     "name": "#%% md\n"
    }
   },
   "source": [
    "We have been using class instances and methods all along..."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'A scanner darkly'"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s = 'A scanner Darkly'\n",
    "s.capitalize()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'apple', 'banana', 'pineapple'}"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x = set(['apple', 'banana', 'apple', 'pineapple'])\n",
    "x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'apple', 'banana', 'kiwi', 'pineapple'}"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x.union(['banana', 'kiwi'])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "pycharm": {
     "name": "#%%\n"
    }
   },
   "outputs": [],
   "source": []
  }
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