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   "source": [
    "### Swapping variable values\n",
    "\n",
    "Suppose"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
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   "source": [
    "a, b = 42, 43"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We've see the following options for swapping their values. One is using multiple assignment:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
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   "outputs": [],
   "source": [
    "a, b = b, a"
   ]
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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Another is using a temporary variable:"
   ]
  },
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   "metadata": {
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   "source": [
    "temp = b\n",
    "b = a\n",
    "a = temp"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Here is how we can swap the values of two integer variables without using either of those tricks:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "a, b = 42, 43\n",
    "\n",
    "#Suppose a == a', b = b'. That is, a' is the \"old\" value of a, and b' is the \"old\" value of b\n",
    "\n",
    "a = a + b  #a == a' + b', b == b'\n",
    "b = a - b  #a == a' + b', b == a'\n",
    "a = a - b  #a == b', b == a'"
   ]
  }
 ],
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