seven_Parser.ipynb

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   "source": [
    "import nltk\n",
    "from nltk import *\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "prob_grammar = nltk.PCFG.fromstring(\"\"\"\n",
    "  S -> NP VP [0.9]| VP  [0.1]\n",
    "  VP -> TranV NP [0.3]\n",
    "  VP -> InV  [0.3]\n",
    "  VP -> DatV NP PP  [0.4]\n",
    "  PP -> P NP   [1.0]\n",
    "  TranV -> \"saw\" [0.2] | \"ate\" [0.2] | \"walked\" [0.2] | \"shot\" [0.2] | \"book\" [0.2]\n",
    "  InV -> \"ate\" [0.5] | \"walked\" [0.5]\n",
    "  DatV -> \"gave\" [0.2] | \"ate\" [0.2] | \"saw\" [0.2] | \"walked\" [0.2] | \"shot\" [0.2]\n",
    "  NP -> Prop [0.2]| Det N [0.4] | Det N PP [0.4]\n",
    "  Prop -> \"John\" [0.25]| \"Mary\" [0.25] | \"Bob\" [0.25] | \"I\" [0.25] \n",
    "  Det -> \"a\" [0.2] | \"an\" [0.2] | \"the\" [0.2] | \"my\" [0.2] | \"that\" [0.2]\n",
    "  N -> \"man\" [0.15] | \"dog\" [0.15] | \"cat\" [0.15] | \"park\" [0.15] | \"telescope\" [0.1] | \"flight\" [0.1] | \"elephant\" [0.1] | \"pajamas\" [0.1]\n",
    "  P -> \"in\" [0.2] | \"on\" [0.2] | \"by\" [0.2] | \"with\" [0.2] | \"through\" [0.2]\n",
    "  \"\"\")\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(S\n",
      "  (NP (Prop John))\n",
      "  (VP (TranV saw) (NP (Det a) (N telescope)))) (p=2.16e-05)\n"
     ]
    }
   ],
   "source": [
    "viterbi_parser = nltk.ViterbiParser(prob_grammar)\n",
    "for tree in viterbi_parser.parse(['John', 'saw', 'a', 'telescope']):\n",
    "    print (tree)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "sentex1 = \"I want a flight through Houston\".split()\n",
    "sentex2 = \"Jack walked with the dog\".split()\n",
    "sentex3 = \"I want to book that flight\".split()\n",
    "sentex4 = \"John gave the dog a bone\".split()\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "flight_grammar = nltk.CFG.fromstring(\"\"\"\n",
    "  S -> NP VP | VP\n",
    "  VP -> V NP | V NP PP\n",
    "  PP -> P NP\n",
    "  V -> \"saw\" | \"ate\" | \"walked\" | \"shot\" | \"book\" | \"want\"\n",
    "  NP -> Prop | Det N | Det N PP\n",
    "  Prop -> \"John\" | \"Mary\" | \"Bob\" | \"I\" | \"Houston\" | \"Jack\"\n",
    "  Det -> \"a\" | \"an\" | \"the\" | \"my\" | \"that\"\n",
    "  N -> \"man\" | \"dog\" | \"cat\" | \"telescope\" | \"park\" | \"elephant\" | \"pajamas\" | \"flight\" \n",
    "  P -> \"in\" | \"on\" | \"by\" | \"with\" | \"through\"\n",
    "  \"\"\")\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(S\n",
      "  (NP (Prop I))\n",
      "  (VP\n",
      "    (V want)\n",
      "    (NP (Det a) (N flight) (PP (P through) (NP (Prop Houston))))))\n",
      "(S\n",
      "  (NP (Prop I))\n",
      "  (VP\n",
      "    (V want)\n",
      "    (NP (Det a) (N flight))\n",
      "    (PP (P through) (NP (Prop Houston)))))\n"
     ]
    }
   ],
   "source": [
    "rd_parser = nltk.RecursiveDescentParser(flight_grammar)\n",
    "for tree in rd_parser.parse(sentex1):\n",
    "    print (tree)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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