toy_inheritance_example.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Raw data that will go into classes later"
   ]
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   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "def svg_surface_draw(self):\n",
    "    print(\"I am svg_surface_draw\")\n",
    "\n",
    "def image_surface_draw(self):\n",
    "    print(\"I am image_surface_draw\")\n",
    "\n",
    "def surface_draw(self):\n",
    "    print(\"I am surface_draw\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Data structure defining what goes into each class"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[{'extends': ['Surface'],\n",
       "  'methods': {'draw': <function __main__.svg_surface_draw>},\n",
       "  'name': 'SvgSurface'},\n",
       " {'extends': ['Surface'],\n",
       "  'methods': {'draw': <function __main__.image_surface_draw>},\n",
       "  'name': 'ImageSurface'},\n",
       " {'methods': {'draw': <function __main__.surface_draw>}, 'name': 'Surface'}]"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "class_definitions = [\n",
    "    dict(name=\"SvgSurface\",  methods=dict(draw=svg_surface_draw), extends=[\"Surface\"]),\n",
    "    dict(name=\"ImageSurface\", methods=dict(draw=image_surface_draw), extends=[\"Surface\"]),\n",
    "    dict(name=\"Surface\", methods=dict(draw=surface_draw))\n",
    "]\n",
    "class_definitions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "Build the class structure from the bottom up.\n",
    "\n",
    "A dictionary of \n",
    "\n",
    "Classes are only built if their base classes have already been built."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
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   "outputs": [],
   "source": [
    "def build_classes(class_definitions):\n",
    "    # Build a dict so we can efficiently remove definitons as classes are built\n",
    "    class_definitions_dict = {\n",
    "        definition['name']: definition for definition in class_definitions\n",
    "    }\n",
    "    built_classes = {}   # name:  Class\n",
    "\n",
    "    while class_definitions_dict:\n",
    "        for data in class_definitions_dict.values():\n",
    "            name, extends, methods = data['name'], data.get('extends', []), data['methods']\n",
    "\n",
    "            if not extends or set(built_classes).issuperset(set(extends)):\n",
    "                # This classes base classes are available so build it\n",
    "\n",
    "                # Grab the base classes from their names\n",
    "                bases = tuple([built_classes[class_name] for class_name in extends])        \n",
    "                klass = type(name, bases, methods)\n",
    "                built_classes[name] = klass\n",
    "\n",
    "                del class_definitions_dict[name]\n",
    "                \n",
    "                globals()[name] = klass\n",
    "\n",
    "build_classes(class_definitions)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<class '__main__.ImageSurface'>\n",
      "<class '__main__.Surface'>\n",
      "<class '__main__.SvgSurface'>\n"
     ]
    }
   ],
   "source": [
    "print(ImageSurface)\n",
    "print(Surface)\n",
    "print(SvgSurface)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Help on class SvgSurface in module __main__:\n",
      "\n",
      "class SvgSurface(Surface)\n",
      " |  Method resolution order:\n",
      " |      SvgSurface\n",
      " |      Surface\n",
      " |      __builtin__.object\n",
      " |  \n",
      " |  Methods defined here:\n",
      " |  \n",
      " |  draw = svg_surface_draw(self)\n",
      " |  \n",
      " |  ----------------------------------------------------------------------\n",
      " |  Data descriptors inherited from Surface:\n",
      " |  \n",
      " |  __dict__\n",
      " |      dictionary for instance variables (if defined)\n",
      " |  \n",
      " |  __weakref__\n",
      " |      list of weak references to the object (if defined)\n",
      "\n"
     ]
    }
   ],
   "source": [
    "help(SvgSurface)  # further info"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I am image_surface_draw\n",
      "I am svg_surface_draw\n"
     ]
    }
   ],
   "source": [
    "surface = ImageSurface()\n",
    "surface.draw()\n",
    "\n",
    "svg_surface = SvgSurface()\n",
    "svg_surface.draw()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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