lazy_decorator_test.ipynb

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   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "See http://stackoverflow.com/questions/3012421/python-lazy-property-decorator#comment33530512_6849299"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def lazyprop(fn):\n",
      "    attr_name = '_lazy_' + fn.__name__\n",
      "    @property\n",
      "    def _lazyprop(self):\n",
      "        if not hasattr(self, attr_name):\n",
      "            setattr(self, attr_name, fn(self))\n",
      "        return getattr(self, attr_name)\n",
      "    return _lazyprop\n",
      "\n",
      "\n",
      "class Test(object):\n",
      "\n",
      "    @lazyprop\n",
      "    def a(self):\n",
      "        print 'generating \"a\"'\n",
      "        return range(5)\n",
      "    \n",
      "t = Test()\n",
      "b = t.a\n",
      "%timeit b = t.a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "generating \"a\"\n",
        "100000 loops, best of 3: 2.45 \u00b5s per loop"
       ]
      },
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "\n"
       ]
      }
     ],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "class lazy_property(object):\n",
      "    '''\n",
      "    meant to be used for lazy evaluation of an object attribute.\n",
      "    property should represent non-mutable data, as it replaces itself.\n",
      "    '''\n",
      "\n",
      "    def __init__(self,fget):\n",
      "        self.fget = fget\n",
      "        self.func_name = fget.__name__\n",
      "\n",
      "\n",
      "    def __get__(self,obj,cls):\n",
      "        if obj is None:\n",
      "            return None\n",
      "        value = self.fget(obj)\n",
      "        setattr(obj,self.func_name,value)\n",
      "        return value\n",
      "class Test(object):\n",
      "\n",
      "    @lazy_property\n",
      "    def a(self):\n",
      "        print 'generating \"a\"'\n",
      "        return range(5)\n",
      "    \n",
      "t = Test()\n",
      "b = t.a    \n",
      "%timeit b = t.a"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "generating \"a\"\n",
        "1000000 loops, best of 3: 322 ns per loop"
       ]
      },
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "\n"
       ]
      }
     ],
     "prompt_number": 1
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
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   "metadata": {}
  }
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