Dumb stuff with operator overloading

String.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "from math import inf\n",
    "class Node(object):\n",
    "    MAX_ATTACHMENTS = inf\n",
    "    \n",
    "    def __init__(self, label=\"Generic Node\"):\n",
    "        self.attachments = []\n",
    "        self.label = label\n",
    "\n",
    "    def _attach(self, other):\n",
    "        if len(self.attachments) >= self.MAX_ATTACHMENTS:\n",
    "            raise ValueError(\"{cls} can only be attached to a maximum of {max} objects.\".format(cls=self.__class__, max=self.MAX_ATTACHMENTS))\n",
    "\n",
    "        if other in self.attachments:\n",
    "            raise Exception(\"Already attached.\")\n",
    "            \n",
    "        self.attachments.append(other)\n",
    "        \n",
    "    def _detach(self, string, called_from=\"node\"):\n",
    "        if string not in self.attachments:\n",
    "            raise ValueError(\"Cannot detach an unattached string.\")\n",
    "        \n",
    "        removed_string = self.attachments.pop(string)\n",
    "\n",
    "        if called_from == \"node\":\n",
    "            removed_string.detach(self, called_from=\"node\")\n",
    "            \n",
    "    def relationship(self, string):\n",
    "        if self == string.start:\n",
    "            return \"beginning of string\"\n",
    "        elif self == string.end:\n",
    "            return \"end of string\"    \n",
    "        else:\n",
    "            raise ValueError(\"No relationship.\")    \n",
    "\n",
    "class Endpoint(Node):\n",
    "    MAX_ATTACHMENTS = 1\n",
    "    \n",
    "    def __init__(self, label=\"Endpoint\"):\n",
    "        super(Endpoint, self).__init__(label=label)\n",
    "\n",
    "class Vertex(Node):\n",
    "    MAX_ATTACHMENTS = 3\n",
    "    \n",
    "    def __init__(self, label=\"Vertex\"):\n",
    "        super(Vertex, self).__init__(label=label)\n",
    "            \n",
    "        \n",
    "class String(object):\n",
    "    @classmethod\n",
    "    def is_node(self, other):\n",
    "        if not isinstance(other, Node):\n",
    "            raise TypeError(\"Strings can only be attached to Node or its subclasses.\")\n",
    "        else:\n",
    "            return True\n",
    "    \n",
    "    def __init__(self, start=None, end=None):\n",
    "        self.start = start\n",
    "        self.end = end\n",
    "\n",
    "    def __radd__(self, other):\n",
    "        \"\"\"\n",
    "        Called when String is on the RH of plus sign: <other> + String().\n",
    "        \n",
    "        Attachment to beginning of string.        \n",
    "        \"\"\"\n",
    "        \n",
    "        assert self.is_node(other)\n",
    "        self.start = other\n",
    "        other._attach(self)\n",
    "        \n",
    "    def __add__(self, other):\n",
    "        \"\"\"\n",
    "        Called when String is on the LH of plus sign: String() + <other>.\n",
    "\n",
    "        Attachment to end of string.\n",
    "        \"\"\"\n",
    "        \n",
    "        assert self.is_node(other)\n",
    "        self.end = other\n",
    "        other._attach(self)\n",
    "\n",
    "    def __rsub__(self, other):\n",
    "        self.detach(self.start)\n",
    "\n",
    "    def __sub__(self, other):\n",
    "        self.detach(self.end)\n",
    "\n",
    "    def detach(self, node, called_from=\"string\"):\n",
    "        if self.start == node:\n",
    "            self.start = None\n",
    "            if called_from == \"string\":\n",
    "                node._detach(self)\n",
    "        elif self.end == node:\n",
    "            self.end = None\n",
    "            if called_from == \"string\":\n",
    "                node._detach(self)\n",
    "        else:\n",
    "            raise ValueError(\"Cannot detach unattached node.\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "v = Vertex(label=\"v1\")\n",
    "e = Endpoint(label=\"e1\")\n",
    "s1 = String()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "v + s1 # Attach to vertex at the start\n",
    "s1 + e # And endpoint at the end"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "('v1', 'e1')"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s1.start.label, s1.end.label"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "([<__main__.String at 0x10a599780>], [<__main__.String at 0x10a599780>])"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "v.attachments, e.attachments "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [],
   "source": [
    "s2 = String()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "<class '__main__.Endpoint'> can only be attached to a maximum of 1 objects.",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-14-9a252a698327>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0me\u001b[0m \u001b[0;34m+\u001b[0m \u001b[0ms2\u001b[0m \u001b[0;31m# Endpoints can fill up\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-3-3520e491b69b>\u001b[0m in \u001b[0;36m__radd__\u001b[0;34m(self, other)\u001b[0m\n\u001b[1;32m     67\u001b[0m         \u001b[0;32massert\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mis_node\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mother\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     68\u001b[0m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mstart\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mother\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 69\u001b[0;31m         \u001b[0mother\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_attach\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     70\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     71\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__add__\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mother\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-3-3520e491b69b>\u001b[0m in \u001b[0;36m_attach\u001b[0;34m(self, other)\u001b[0m\n\u001b[1;32m      9\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m_attach\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mother\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     10\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0mlen\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mattachments\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;34m>=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mMAX_ATTACHMENTS\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 11\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mValueError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"{cls} can only be attached to a maximum of {max} objects.\"\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mformat\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mcls\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m__class__\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mmax\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mMAX_ATTACHMENTS\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     12\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     13\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0mother\u001b[0m \u001b[0;32min\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mattachments\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mValueError\u001b[0m: <class '__main__.Endpoint'> can only be attached to a maximum of 1 objects."
     ]
    }
   ],
   "source": [
    "e + s2 # Endpoints can fill up"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[<__main__.String at 0x10a599780>, <__main__.String at 0x10a5941d0>]"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "v + s2 # But vertices haven't yet\n",
    "v.attachments"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'beginning of string'"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "v.relationship(s2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "s3 = String()\n",
    "s3 + v"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'end of string'"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "v.relationship(s3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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