LazyDictionary.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 91,
   "metadata": {},
   "outputs": [],
   "source": [
    "import collections\n",
    "import random\n",
    "\n",
    "class LazyEntries(collections.abc.Mapping):\n",
    "    \n",
    "    def __init__(self, dictionary=None):\n",
    "        self._dict = dictionary or {}\n",
    "        \n",
    "    def __getitem__(self, key):\n",
    "        if callable(self._dict[key]):\n",
    "            result = self._dict[key].__call__()\n",
    "            self._dict[key] = result\n",
    "            return result\n",
    "        else:\n",
    "            return self._dict[key]\n",
    "        \n",
    "    def __setitem__(self, key, value):\n",
    "        self._dict[key] = value\n",
    "    \n",
    "    def __iter__(self):\n",
    "        return iter(self._dict)\n",
    "\n",
    "    def __len__(self):\n",
    "        return len(self._dict)\n",
    "\n",
    "class Entry:\n",
    "    def __init__(self, name):\n",
    "        print(\"init\", name)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 96,
   "metadata": {},
   "outputs": [],
   "source": [
    "d = {key: lambda: Entry(4) for key in range(10)}\n",
    "lm = LazyEntries(d)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 87,
   "metadata": {
    "scrolled": true
   },
   "outputs": [],
   "source": [
    "lm[1] = lambda: A('G')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 88,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "init G\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "<__main__.A at 0x7f26309a3358>"
      ]
     },
     "execution_count": 88,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "lm[1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 89,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]"
      ]
     },
     "execution_count": 89,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "list(lm)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 97,
   "metadata": {},
   "outputs": [],
   "source": [
    "entries = LazyEntries()\n",
    "\n",
    "for i in range(10):\n",
    "    entries[i] = lambda: Entry(random.randint(0,10))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 98,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<__main__.LazyEntries at 0x7f2630a188d0>"
      ]
     },
     "execution_count": 98,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "entries"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 99,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]"
      ]
     },
     "execution_count": 99,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "list(entries)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 100,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "init 5\n",
      "init 9\n",
      "init 4\n",
      "init 8\n",
      "init 5\n",
      "init 5\n",
      "init 9\n",
      "init 2\n",
      "init 2\n",
      "init 2\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "[(0, <__main__.Entry at 0x7f2630a180f0>),\n",
       " (1, <__main__.Entry at 0x7f2630a0a6a0>),\n",
       " (2, <__main__.Entry at 0x7f26309bf198>),\n",
       " (3, <__main__.Entry at 0x7f2630a0aa90>),\n",
       " (4, <__main__.Entry at 0x7f2630a0a710>),\n",
       " (5, <__main__.Entry at 0x7f2630a0a5c0>),\n",
       " (6, <__main__.Entry at 0x7f2630a0a2b0>),\n",
       " (7, <__main__.Entry at 0x7f2630a0a4e0>),\n",
       " (8, <__main__.Entry at 0x7f2630a0a1d0>),\n",
       " (9, <__main__.Entry at 0x7f2630a0a320>)]"
      ]
     },
     "execution_count": 100,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "list(entries.items())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.7.3"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}