08-object-oriented-programming/08.08-inheritance.ipynb

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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 继承"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "一个类定义的基本形式如下：\n",
    "```python\n",
    "class ClassName(ParentClass):\n",
    "    \"\"\"class docstring\"\"\"\n",
    "    def method(self):\n",
    "        return\n",
    "```\n",
    "\n",
    "- `class` 关键词在最前面\n",
    "- `ClassName` 通常采用 `CamelCase` 记法\n",
    "- 括号中的 `ParentClass` 用来表示继承关系\n",
    "- 冒号不能缺少\n",
    "- `\"\"\"\"\"\"` 中的内容表示 `docstring`，可以省略\n",
    "- 方法定义与函数定义十分类似，不过多了一个 `self` 参数表示这个对象本身\n",
    "- `class` 中的方法要进行缩进\n",
    "\n",
    "在里面有一个 `ParentClass` 项，用来进行继承，被继承的类是父类，定义的这个类是子类。\n",
    "对于子类来说，继承意味着它可以使用所有父类的方法和属性，同时还可以定义自己特殊的方法和属性。\n",
    "\n",
    "假设我们有这样一个父类："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class Leaf(object):\n",
    "    def __init__(self, color=\"green\"):\n",
    "        self.color = color\n",
    "    def fall(self):\n",
    "        print \"Splat!\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "测试："
   ]
  },
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   "execution_count": 2,
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "green\n"
     ]
    }
   ],
   "source": [
    "leaf = Leaf()\n",
    "\n",
    "print leaf.color"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Splat!\n"
     ]
    }
   ],
   "source": [
    "leaf.fall()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "现在定义一个子类，继承自 `Leaf`："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class MapleLeaf(Leaf):\n",
    "    def change_color(self):\n",
    "        if self.color == \"green\":\n",
    "            self.color = \"red\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "继承父类的所有方法："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "green\n"
     ]
    }
   ],
   "source": [
    "mleaf = MapleLeaf()\n",
    "\n",
    "print mleaf.color"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Splat!\n"
     ]
    }
   ],
   "source": [
    "mleaf.fall()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "但是有自己独有的方法，父类中没有："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "red\n"
     ]
    }
   ],
   "source": [
    "mleaf.change_color()\n",
    "\n",
    "print mleaf.color"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "如果想对父类的方法进行修改，只需要在子类中重定义这个类即可："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class MapleLeaf(Leaf):\n",
    "    def change_color(self):\n",
    "        if self.color == \"green\":\n",
    "            self.color = \"red\"\n",
    "    def fall(self):\n",
    "        self.change_color()\n",
    "        print \"Plunk!\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false,
    "scrolled": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "green\n",
      "Plunk!\n",
      "red\n"
     ]
    }
   ],
   "source": [
    "mleaf = MapleLeaf()\n",
    "\n",
    "print mleaf.color\n",
    "mleaf.fall()\n",
    "print mleaf.color"
   ]
  }
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