item_08-Avoid	More	Than	Two	Expressions	in	List Comprehensions.ipynb

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    "# 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": [
    "### support\tmultiple\tlevels\tof\tlooping!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5, 6, 7, 8, 9]\n"
     ]
    }
   ],
   "source": [
    "# Example 1\n",
    "matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]\n",
    "flat = [x for row in matrix for x in row]\n",
    "print(flat)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### two-dimensional\tmatrix, but still readable."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[[1, 4, 9], [16, 25, 36], [49, 64, 81]]\n"
     ]
    }
   ],
   "source": [
    "# Example 2\n",
    "squared = [[x**2 for x in row] for row in matrix]\n",
    "print(squared)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### another\tloop? Getting complicated!!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]\n"
     ]
    }
   ],
   "source": [
    "# Example 3\n",
    "my_lists = [\n",
    "    [[1, 2, 3], [4, 5, 6]],\n",
    "    [[7, 8, 9], [10, 11, 12]],\n",
    "]\n",
    "flat = [x for sublist1 in my_lists\n",
    "        for sublist2 in sublist1\n",
    "        for x in sublist2]\n",
    "print(flat)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Perhaps, using loops is better."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]\n"
     ]
    }
   ],
   "source": [
    "# Example 4\n",
    "flat = []\n",
    "for sublist1 in my_lists:\n",
    "    for sublist2 in sublist1:\n",
    "        flat.extend(sublist2)\n",
    "print(flat)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[6, 8, 10]\n",
      "[6, 8, 10]\n"
     ]
    }
   ],
   "source": [
    "# Example 5\n",
    "a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]\n",
    "b = [x for x in a if x > 4 if x % 2 == 0]\n",
    "c = [x for x in a if x > 4 and x % 2 == 0]\n",
    "print(b)\n",
    "print(c)\n",
    "assert b and c\n",
    "assert b == c"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### It's short, but hard to read. Void if possible. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[[6], [9]]\n"
     ]
    }
   ],
   "source": [
    "# Example 6\n",
    "matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]\n",
    "filtered = [[x for x in row if x % 3 == 0]\n",
    "            for row in matrix if sum(row) >= 10]\n",
    "print(filtered)"
   ]
  }
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