08-object-oriented-programming/08.04-writing-classes.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 定义 class"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 基本形式"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`class` 定义如下：\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"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class Forest(object):\n",
    "    \"\"\" Forest can grow trees which eventually die.\"\"\"\n",
    "    pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "其中 `object` 是最基本的类型。\n",
    "\n",
    "查看帮助："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " Forest()\n",
      "\n",
      "Forest can grow trees which eventually die.\n",
      "\n",
      "\n",
      "Methods:\n",
      "\n"
     ]
    }
   ],
   "source": [
    "import numpy as np\n",
    "np.info(Forest)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "forest = Forest()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<__main__.Forest at 0x3cda358>"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "forest"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 添加方法和属性"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "可以直接添加属性（有更好的替代方式）："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "forest.trees = np.zeros((150, 150), dtype=bool)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([[False, False, False, ..., False, False, False],\n",
       "       [False, False, False, ..., False, False, False],\n",
       "       [False, False, False, ..., False, False, False],\n",
       "       ..., \n",
       "       [False, False, False, ..., False, False, False],\n",
       "       [False, False, False, ..., False, False, False],\n",
       "       [False, False, False, ..., False, False, False]], dtype=bool)"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "forest.trees"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "forest2 = Forest()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`forest2` 没有这个属性："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'Forest' object has no attribute 'trees'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-8-42e6a9d57a8b>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mforest2\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mtrees\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mAttributeError\u001b[0m: 'Forest' object has no attribute 'trees'"
     ]
    }
   ],
   "source": [
    "forest2.trees"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "添加方法时，默认第一个参数是对象本身，一般为 `self`，可能用到也可能用不到，然后才是其他的参数："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "class Forest(object):\n",
    "    \"\"\" Forest can grow trees which eventually die.\"\"\"\n",
    "    def grow(self):\n",
    "        print \"the tree is growing!\"\n",
    "        \n",
    "    def number(self, num=1):\n",
    "        if num == 1:\n",
    "            print 'there is 1 tree.'\n",
    "        else:\n",
    "            print 'there are', num, 'trees.'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "the tree is growing!\n",
      "there are 12 trees.\n"
     ]
    }
   ],
   "source": [
    "forest = Forest()\n",
    "\n",
    "forest.grow()\n",
    "forest.number(12)"
   ]
  }
 ],
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