{
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  {
   "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": [
    "## From other language, we love to use getter and setter, but not in Python!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 1\n",
    "class OldResistor(object):\n",
    "    def __init__(self, ohms):\n",
    "        self._ohms = ohms\n",
    "\n",
    "    def get_ohms(self):\n",
    "        return self._ohms\n",
    "\n",
    "    def set_ohms(self, ohms):\n",
    "        self._ohms = ohms"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before: 50000.0\n",
      "After:  10000.0\n"
     ]
    }
   ],
   "source": [
    "# Example 2\n",
    "r0 = OldResistor(50e3)\n",
    "print('Before: %5r' % r0.get_ohms())\n",
    "r0.set_ohms(10e3)\n",
    "print('After:  %5r' % r0.get_ohms())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 3\n",
    "r0.set_ohms(r0.get_ohms() + 5e3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Just use simple\tpublic\tattributes"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "10000.0 ohms, 0 volts, 0 amps\n"
     ]
    }
   ],
   "source": [
    "# Example 4\n",
    "class Resistor(object):\n",
    "    def __init__(self, ohms):\n",
    "        self.ohms = ohms\n",
    "        self.voltage = 0\n",
    "        self.current = 0\n",
    "\n",
    "r1 = Resistor(50e3)\n",
    "r1.ohms = 10e3\n",
    "print('%r ohms, %r volts, %r amps' %\n",
    "      (r1.ohms, r1.voltage, r1.current))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 5\n",
    "r1.ohms += 5e3"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 6\n",
    "class VoltageResistance(Resistor):\n",
    "    def __init__(self, ohms):\n",
    "        super().__init__(ohms)\n",
    "        self._voltage = 0\n",
    "\n",
    "    @property\n",
    "    def voltage(self):\n",
    "        return self._voltage\n",
    "\n",
    "    @voltage.setter\n",
    "    def voltage(self, voltage):\n",
    "        self._voltage = voltage\n",
    "        self.current = self._voltage / self.ohms"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before:     0 amps\n",
      "After:   0.01 amps\n"
     ]
    }
   ],
   "source": [
    "# Example 7\n",
    "r2 = VoltageResistance(1e3)\n",
    "print('Before: %5r amps' % r2.current)\n",
    "r2.voltage = 10\n",
    "print('After:  %5r amps' % r2.current)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## \t@property\tdecorator\tand\tits\tcorresponding\tsetter\tattribute? Why??"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 8\n",
    "class BoundedResistance(Resistor):\n",
    "    def __init__(self, ohms):\n",
    "        super().__init__(ohms)\n",
    "\n",
    "    @property\n",
    "    def ohms(self):\n",
    "        return self._ohms\n",
    "\n",
    "    @ohms.setter\n",
    "    def ohms(self, ohms):\n",
    "        if ohms <= 0:\n",
    "            raise ValueError('%f ohms must be > 0' % ohms)\n",
    "        self._ohms = ohms"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 9\n",
    "try:\n",
    "    r3 = BoundedResistance(1e3)\n",
    "    r3.ohms = 0\n",
    "except:\n",
    "    logging.exception('Expected')\n",
    "else:\n",
    "    assert False"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 10\n",
    "try:\n",
    "    BoundedResistance(-5)\n",
    "except:\n",
    "    logging.exception('Expected')\n",
    "else:\n",
    "    assert False"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 11\n",
    "class FixedResistance(Resistor):\n",
    "    def __init__(self, ohms):\n",
    "        super().__init__(ohms)\n",
    "\n",
    "    @property\n",
    "    def ohms(self):\n",
    "        return self._ohms\n",
    "\n",
    "    @ohms.setter\n",
    "    def ohms(self, ohms):\n",
    "        if hasattr(self, '_ohms'):\n",
    "            raise AttributeError(\"Can't set attribute\")\n",
    "        self._ohms = ohms"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 12\n",
    "try:\n",
    "    r4 = FixedResistance(1e3)\n",
    "    r4.ohms = 2e3\n",
    "except:\n",
    "    logging.exception('Expected')\n",
    "else:\n",
    "    assert False"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 13\n",
    "class MysteriousResistor(Resistor):\n",
    "    @property\n",
    "    def ohms(self):\n",
    "        self.voltage = self._ohms * self.current\n",
    "        return self._ohms\n",
    "\n",
    "    @ohms.setter\n",
    "    def ohms(self, ohms):\n",
    "        self._ohms = ohms"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before:     0\n",
      "After:    0.1\n"
     ]
    }
   ],
   "source": [
    "# Example 14\n",
    "r7 = MysteriousResistor(10)\n",
    "r7.current = 0.01\n",
    "print('Before: %5r' % r7.voltage)\n",
    "r7.ohms\n",
    "print('After:  %5r' % r7.voltage)"
   ]
  }
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