{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Comprehensions are good, but not memory efficient. They may create\ta\twhole\tnew\tlist"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Copyright 2014 Brett Slatkin, Pearson Education Inc.\n",
    "#\n",
    "# Licensed under the Apache License, Version 2.0 (the \"License\");\n",
    "# you may not use this file except in compliance with the License.\n",
    "# You may obtain a copy of the License at\n",
    "#\n",
    "#     http://www.apache.org/licenses/LICENSE-2.0\n",
    "#\n",
    "# Unless required by applicable law or agreed to in writing, software\n",
    "# distributed under the License is distributed on an \"AS IS\" BASIS,\n",
    "# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n",
    "# See the License for the specific language governing permissions and\n",
    "# limitations under the License.\n",
    "\n",
    "# Preamble to mimick book environment\n",
    "import logging\n",
    "from pprint import pprint\n",
    "from sys import stdout as STDOUT"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Need to \thold the\tlength\tof\tevery\tline\tof\tthe file\tin\tmemory. BAD!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[94, 48, 19, 7, 27, 36, 92, 33, 25, 9]\n"
     ]
    }
   ],
   "source": [
    "# Example 1\n",
    "import random\n",
    "with open('my_file.txt', 'w') as f:\n",
    "    for _ in range(10):\n",
    "        f.write('a' * random.randint(0, 100))\n",
    "        f.write('\\n')\n",
    "\n",
    "value = [len(x) for x in open('my_file.txt')]\n",
    "print(value)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### A\tgenerator\texpression () does not make forward progress. GOOD!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<generator object <genexpr> at 0x103e45e08>\n"
     ]
    }
   ],
   "source": [
    "# Example 2\n",
    "it = (len(x) for x in open('my_file.txt'))\n",
    "print(it)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "### It returns iterator."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "94\n",
      "48\n"
     ]
    }
   ],
   "source": [
    "# Example 3\n",
    "print(next(it))\n",
    "print(next(it))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### generator\texpressions\tcan\tbe\tcomposed\ttogether. Create a new generator using 'it'! WONDERFUL!!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<generator object <genexpr> at 0x103e45eb8>\n"
     ]
    }
   ],
   "source": [
    "# Example 4\n",
    "roots = ((x, x**0.5) for x in it)\n",
    "print(roots)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(19, 4.358898943540674)\n"
     ]
    }
   ],
   "source": [
    "# Example 5\n",
    "print(next(roots))"
   ]
  }
 ],
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