foo

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 "metadata": {
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  "signature": "sha256:da85fe4b1722ac997645f8af9888f4c3bae14dd9cb630421133dcfa6372ef829"
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 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def arrange(items, count):\n",
      "    if count == 0:\n",
      "        return []\n",
      "#     print \"choose() items: \"+str(items)+\", count: \"+str(count)\n",
      "    res = []\n",
      "    i = 0\n",
      "    for item in items:\n",
      "        subres = arrange(items[:i]+items[i+1:], count - 1)\n",
      "        if not subres:\n",
      "            res.append([item])\n",
      "        for rest in subres:\n",
      "            res.append([item] + rest)\n",
      "        i += 1\n",
      "            \n",
      "    return res\n",
      "def print_sets(sets):\n",
      "    for subset in sets:\n",
      "        print subset\n",
      "print_sets(arrange(['a', 'b', 'c', 'd'], 4))"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "['a', 'b', 'c', 'd']\n",
        "['a', 'b', 'd', 'c']\n",
        "['a', 'c', 'b', 'd']\n",
        "['a', 'c', 'd', 'b']\n",
        "['a', 'd', 'b', 'c']\n",
        "['a', 'd', 'c', 'b']\n",
        "['b', 'a', 'c', 'd']\n",
        "['b', 'a', 'd', 'c']\n",
        "['b', 'c', 'a', 'd']\n",
        "['b', 'c', 'd', 'a']\n",
        "['b', 'd', 'a', 'c']\n",
        "['b', 'd', 'c', 'a']\n",
        "['c', 'a', 'b', 'd']\n",
        "['c', 'a', 'd', 'b']\n",
        "['c', 'b', 'a', 'd']\n",
        "['c', 'b', 'd', 'a']\n",
        "['c', 'd', 'a', 'b']\n",
        "['c', 'd', 'b', 'a']\n",
        "['d', 'a', 'b', 'c']\n",
        "['d', 'a', 'c', 'b']\n",
        "['d', 'b', 'a', 'c']\n",
        "['d', 'b', 'c', 'a']\n",
        "['d', 'c', 'a', 'b']\n",
        "['d', 'c', 'b', 'a']\n"
       ]
      }
     ],
     "prompt_number": 48
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "a = [1, 2, 3, 4, 5]\n",
      "a[:2]+ a[3:]"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 29,
       "text": [
        "[1, 2, 4, 5]"
       ]
      }
     ],
     "prompt_number": 29
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
}