autovivication

autovivication.json

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    "class AutoVivication(dict):\n",
    "    \"\"\"\n",
    "    Adding new key without value creates new AutoVivication as value allowing nested dictionary creation in one line.\n",
    "    \n",
    "    >>> a = AutoVivication()\n",
    "    >>> a[1][2]['test'] = [3, 4, 5]\n",
    "    {1: {2: {'test': [3, 4, 5]}}}\n",
    "    \"\"\"\n",
    "    def __getitem__(self, key):\n",
    "        \"\"\"\n",
    "        Overide dict.__getitem__()\n",
    "        \n",
    "        If key is already in dictionary, return it. Otherwise autovivacate; i.e. create new key-value pair by calling\n",
    "        base dict.__setitem__(self, key, AutoVivication())\n",
    "        \"\"\"\n",
    "        print '\\n> inside __getitem__'\n",
    "        \n",
    "        try:\n",
    "            # try base dict.__getitem__() method\n",
    "            print '> checking if key, \"%r\", is in this AutoVivication' % key\n",
    "            return dict.__getitem__(self, key)\n",
    "        \n",
    "        except KeyError:\n",
    "            # key did not exist\n",
    "            print '> key, \"%r\",  did not exist' % key\n",
    "            print '> creating new empty AutoVivication inside this current AutoVivication at key, \"%r\"' % key\n",
    "            # call base dict.__setitem__() method\n",
    "            # use introspection to refer to parent class (AutoVivication) without naming it explicitly, thus making the code\n",
    "            #   more maintainable.\n",
    "            \n",
    "            self[key] = value = type(self)()  # type(self)() is equivalent to self.__class__()\n",
    "            # reads from right to left\n",
    "            # >>> value = self.__class__() # create a new AutoVivication object\n",
    "            # >>> self.__setitem__(key, value) # set key-value pair\n",
    "            #\n",
    "            # __setitem__() returns None, so must cache value to return it\n",
    "            # since __setitem__() is not overridden, dict.__setitem__(self, key, value) is equivalent to\n",
    "            #   self.__setitem__(key, value)\n",
    "            \n",
    "            # return new empty AutoVivication\n",
    "            print 'return new empty AutoVivcation, \"%r\"\\n' % value\n",
    "            return value"
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     "text": [
      "a = {}\n"
     ]
    }
   ],
   "source": [
    "a = AutoVivication()  # new autovivcation class object\n",
    "print 'a = %r' % a"
   ]
  },
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   "execution_count": 3,
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     "text": [
      "\n",
      "> inside __getitem__\n",
      "> checking if key, \"1\", is in this AutoVivication\n",
      "> key, \"1\",  did not exist\n",
      "> creating new empty AutoVivication inside this current AutoVivication at key, \"1\"\n",
      "return new empty AutoVivcation, \"{}\"\n",
      "\n",
      "\n",
      "> inside __getitem__\n",
      "> checking if key, \"2\", is in this AutoVivication\n",
      "> key, \"2\",  did not exist\n",
      "> creating new empty AutoVivication inside this current AutoVivication at key, \"2\"\n",
      "return new empty AutoVivcation, \"{}\"\n",
      "\n",
      "a = {1: {2: {'foo': [5, 6, 7]}}}\n"
     ]
    }
   ],
   "source": [
    "a[1][2]['foo'] = [5, 6, 7]  # autovivicate a[1] and a[1][2], then set a[1][2]['foo'] to [5, 6, 7]\n",
    "print 'a = %r' % a"
   ]
  },
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   "cell_type": "code",
   "execution_count": 4,
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    "collapsed": false,
    "scrolled": false
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     "output_type": "stream",
     "text": [
      "\n",
      "> inside __getitem__\n",
      "> checking if key, \"1\", is in this AutoVivication\n",
      "\n",
      "> inside __getitem__\n",
      "> checking if key, \"2\", is in this AutoVivication\n",
      "a = {1: {2: {'foo': [5, 6, 7], 'bar': [0.1, 0.2, 0.3]}}}\n"
     ]
    }
   ],
   "source": [
    "a[1][2]['bar'] = [0.1, 0.2, 0.3]  # autovivicates a[4] then set a[1][2]['bar'] to [0.1, 0.2, 0.3]\n",
    "print 'a = %r' % a"
   ]
  },
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   "cell_type": "code",
   "execution_count": null,
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