using `__init_subclass__` and `__new__` to do cool things!

layer_view.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Layer:\n",
    "    def __repr__(self):\n",
    "        return f'{type(self).__name__}()'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "class ImageLayer(Layer): ..."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "_subclass_layer_maps = {}\n",
    "\n",
    "\n",
    "class LayerView:\n",
    "    def __new__(cls, layer):\n",
    "        if cls is LayerView:\n",
    "            raise TypeError(f'cannot instantiate {LayerView.__name__} class')\n",
    "\n",
    "        try:\n",
    "            cls = _subclass_layer_maps[cls][type(layer)]\n",
    "        except KeyError:\n",
    "            pass\n",
    "\n",
    "        return object.__new__(cls)\n",
    "\n",
    "    def __init_subclass__(cls, layer=None, **kwargs):\n",
    "        maps = _subclass_layer_maps\n",
    "        \n",
    "        for subclass in maps:\n",
    "            if issubclass(cls, subclass):\n",
    "                if issubclass(layer, Layer):\n",
    "                    maps[subclass][layer] = cls\n",
    "                break\n",
    "        else:\n",
    "            maps[cls] = {}\n",
    "        \n",
    "        super().__init_subclass__(**kwargs)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "class QtLayerProperties(LayerView):\n",
    "    def __init__(self, layer):\n",
    "        self.layer = layer\n",
    "        \n",
    "    def __repr__(self):\n",
    "        return f'{type(self).__name__}({repr(self.layer)})'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
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     "data": {
      "text/plain": [
       "{__main__.QtLayerProperties: {}}"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
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    "_subclass_layer_maps"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [],
   "source": [
    "class QtImageProperties(QtLayerProperties, layer=ImageLayer): ..."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{__main__.QtLayerProperties: {__main__.ImageLayer: __main__.QtImageProperties}}"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "_subclass_layer_maps"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "QtImageProperties(ImageLayer())"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "QtLayerProperties(ImageLayer())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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