Python Regular Expressions Made Easy -  Part 17 - Variable Width Assertions with Look Behinds.ipynb

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   "source": [
    "import re"
   ]
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  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   "outputs": [],
   "source": [
    "#Revisit earlier examples"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
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   "source": [
    "string ='''1111    ABCC    77777777    active\n",
    "           2222    ABC     88888888    inactive\n",
    "           3333    XYZ     xxxxxxxx    active\n",
    "           4444    1234    20351118    inactive  \n",
    "           5555    1445    20153318    inactive  \n",
    "\n",
    "           '''\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "pattern =re.compile('(?<=[A-Z]+)[A-Z]+\\s+(\\S+)') #look behind # look-behind requires fixed-width pattern\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "import regex"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "pattern =regex.compile('(?<=[A-Z]+)[A-Z]+\\s+(\\S+)')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['77777777', '88888888', 'xxxxxxxx']"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "regex.findall(pattern, string)"
   ]
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  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": []
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  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "s= 'C:\\Tools\\System32\\calc.exe'\n",
    "s2= 'C:\\Windows\\System32\\calc.exe'\n",
    "s3= 'C:\\Windows\\System32\\De-de\\calc.exe'\n",
    "s4= 'C:\\Tools\\calc.exe'\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "pattern =re.compile(r'(?<!System32.*)calc.exe') #error"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "pattern =regex.compile(r'(?<!System32.*)calc.exe')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['calc.exe']"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "regex.findall(pattern, s4)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "s= 'C:\\Tools\\System32\\calc.exe'"
   ]
  }
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