machinelearning_notebook/0_python/7_Class.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 类"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Python中的变量、列表、字典等其实都是类，因为Python从设计之初就已经是一门面向对象的语言。\n",
    "\n",
    "本节常见的定义和概念定义：\n",
    "* 类(Class): 用来描述具有相同的属性和方法的对象的集合。它定义了该集合中每个对象所共有的属性和方法。对象是类的实例。\n",
    "* 对象：通过类定义的数据结构实例。对象包括两个数据成员（类变量和实例变量）和方法。例如我们定义了一个 `Person` 类，而具体的人，比如小明，小黄就是 `Person` 类的实例\n",
    "* 属性: 描述该类具有的特征，比如人类具备的属性，身份证，姓名，性别，身高，体重等等都是属性\n",
    "* 方法:是该类对象的行为，例如这个男孩会打篮球，那个女孩会唱歌等等都是属于方法，常常通过方法改变一些类中的属性值"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "类声明如下:"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```\n",
    "class class_name:\n",
    "\n",
    "    Functions\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 一个最简单的类\n",
    "class FirstClass:\n",
    "    pass\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**pass** 在Python中意味着什么都不做。 "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "上面声明了一个名为“FirstClass”的类对象，现在考虑一个具有“FirstClass”所有特征的“egclass”。所以你所要做的就是，将“egclass”等同于“FirstClass”。在python术语中，这称为创建实例。“egclass”是“FirstClass”的实例"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "egclass = FirstClass()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "__main__.FirstClass"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "type(egclass)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "type"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "type(FirstClass)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "现在让我们向类中添加一些“功能”。这样我们的FirstClass就有了更好的定义。类内的函数被称为该类的“方法”"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "大多数类都有一个名为`__init__`的函数。这些被称为魔术方法。在这个方法中，你基本上初始化了这个类的变量，或者任何适用于这个方法中指定的所有方法的初始化算法。类中的变量称为属性。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "当构造函数被定义后，`__init__`被调用，这样初始化实例被创建。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "我们构造我们的`FirstClass`去接受两个变量名称和符号。\n",
    "\n",
    "我将会在稍后解释`self`。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "class FirstClass:\n",
    "    \"\"\"My first class\"\"\"\n",
    "    class_var = 10\n",
    "    def __init__(self,name,value):\n",
    "        self.name = name\n",
    "        self.value = value"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "现在我们已经定义了一个函数而且添加了`__init__`方法。我们可以创建一个名为FirstClass的实例，该实例现在接受两个参数。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "eg1 = FirstClass('one',1)\n",
    "eg2 = FirstClass('two',2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "one 1\n",
      "two 2\n",
      "My first class\n"
     ]
    }
   ],
   "source": [
    "print(eg1.name, eg1.value)\n",
    "print(eg2.name, eg2.value)\n",
    "print(eg1.__doc__)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**dir( )** 函数在查看类包含什么以及它提供了什么方法时非常方便。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "scrolled": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'class_var']"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(FirstClass)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'My first class'"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "FirstClass.__doc__"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "实例的**dir()** 也显示了它定义的属性。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'class_var',\n",
       " 'name',\n",
       " 'value']"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(eg1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "稍微改变一下FirstClass函数，"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [],
   "source": [
    "class FirstClass:\n",
    "    def __init__(self,name,value):\n",
    "        self.n = name\n",
    "        self.v = value"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "将self.name和self.symbol转化成self.n和self.s会得到："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "eg1 = FirstClass('one',1)\n",
    "eg2 = FirstClass('two',2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'FirstClass' object has no attribute 'name'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-15-4ab7dec1c737>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0meg1\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mname\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0meg1\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0msymbol\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      2\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0meg2\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mname\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0meg2\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0msymbol\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mAttributeError\u001b[0m: 'FirstClass' object has no attribute 'name'"
     ]
    }
   ],
   "source": [
    "print(eg1.name, eg1.symbol)\n",
    "print(eg2.name, eg2.symbol)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "AttributeError, 还记得变量就是类中的属性吗?因此，这意味着我们没有为实例提供正确的属性。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'n',\n",
       " 'v']"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(eg1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "one 1\n",
      "two 2\n"
     ]
    }
   ],
   "source": [
    "print(eg1.n, eg1.v)\n",
    "print(eg2.n, eg2.v)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "现在我们解决了这个错误。现在让我们比较一下我们看到的两个例子。\n",
    "\n",
    "当我声明self.name和self.value，使用eg1.name和eg1.value没有属性错误。当我声明self.n和self.s时，使用eg1.n和eg1.s没有属性错误。\n",
    "\n",
    "从以上我们可以得出**self**就是实例本身。\n",
    "\n",
    "记住，**self**不是Python的关键词，它是用户定义的。你可以利用任何你觉得舒服的东西。但是使用self已经成为一种常见的做法。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "class FirstClass:\n",
    "    def __init__(asdf1234,name,value):\n",
    "        asdf1234.n = name\n",
    "        asdf1234.v = value"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [],
   "source": [
    "eg1 = FirstClass('one',1)\n",
    "eg2 = FirstClass('two',2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "one 1\n",
      "two 2\n"
     ]
    }
   ],
   "source": [
    "print(eg1.n, eg1.v)\n",
    "print(eg2.n, eg2.v)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "因为eg1和eg2是FirstClass的实例，所以它不需要被限制在FirstClass本身。它可以通过声明其他属性来扩展自己，而不需要在FirstClass中声明属性。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [],
   "source": [
    "eg1.cube = 1\n",
    "eg2.cube = 8"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'cube',\n",
       " 'n',\n",
       " 'v']"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(eg1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "就像我们前面看到的全局变量和局部变量一样，即使类也有自己的变量类型。\n",
    "\n",
    "**类属性**:在方法外部定义的属性，适用于所有实例。\n",
    "\n",
    "**实例属性**:在方法内部定义的属性，只适用于该方法，并且对每个实例都是唯一的。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [],
   "source": [
    "class FirstClass:\n",
    "    test = 'test'\n",
    "    def __init__(self,name,value):\n",
    "        self.name = name\n",
    "        self.value = value"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "这里test是一个类属性，而name是一个实例属性。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "test4\n"
     ]
    }
   ],
   "source": [
    "eg3 = FirstClass('Three',3)\n",
    "eg4 = FirstClass('Four', 4)\n",
    "eg4.test = 'test4'\n",
    "print(eg4.test)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "test Three\n"
     ]
    }
   ],
   "source": [
    "print(eg3.test, eg3.name)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "让我们添加更多的方法到FirstClass。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [],
   "source": [
    "class FirstClass:\n",
    "    def __init__(self,name,value):\n",
    "        self.name = name\n",
    "        self.value = value\n",
    "    def square(self):\n",
    "        return self.value * self.value\n",
    "    def cube(self):\n",
    "        return self.value * self.value * self.value\n",
    "    def multiply(self, x):\n",
    "        return self.value * x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [],
   "source": [
    "eg4 = FirstClass('Five',5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "25\n",
      "125\n"
     ]
    }
   ],
   "source": [
    "print(eg4.square())\n",
    "print(eg4.cube())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 27,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "eg4.multiply(2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "以上也可以写成："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 28,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "FirstClass.multiply(eg4,2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2. 继承"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "在某些情况下，新类需要具有已定义类的所有特征。因此，新类可以“继承”前一个类，并向其添加自己的方法，这称为继承。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "考虑类Person类具有薪水的方法。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Person:\n",
    "    def __init__(self,name,age):\n",
    "        self.name = name\n",
    "        self.age = age\n",
    "    def salary(self, value):\n",
    "        self.money = value\n",
    "        print(self.name,\"earns\",self.money)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = Person('Jerry',26)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Jerry earns 40000\n"
     ]
    }
   ],
   "source": [
    "a.salary(40000)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'salary']"
      ]
     },
     "execution_count": 32,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(Person)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "现在考虑另一个Artist类，告诉我们艺术家挣的钱的数量和他的艺术形式。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Artist:\n",
    "    def __init__(self,name,age):\n",
    "        self.name = name\n",
    "        self.age = age\n",
    "    def salary(self,value):\n",
    "        self.money = value\n",
    "        print(self.name,\"earns\",self.money)\n",
    "    def artform(self, job):\n",
    "        self.job = job\n",
    "        print(self.name,\"is a\", self.job)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {},
   "outputs": [],
   "source": [
    "b = Artist('Nick',20)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Nick earns 50000\n",
      "Nick is a Musician\n"
     ]
    }
   ],
   "source": [
    "b.salary(50000)\n",
    "b.artform('Musician')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'artform',\n",
       " 'salary']"
      ]
     },
     "execution_count": 37,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(Artist)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "money 方法和salary 方法是一样的。因此，我们可以将该方法推广到工资类，并将软件工程师类继承到美术师类。现在艺术类变成了，"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 38,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Artist(Person):\n",
    "    def artform(self, job):\n",
    "        self.job = job\n",
    "        print(self.name,\"is a\", self.job)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 40,
   "metadata": {},
   "outputs": [],
   "source": [
    "c = Artist('Tom',21)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 41,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'artform',\n",
       " 'salary']"
      ]
     },
     "execution_count": 41,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dir(Artist)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 42,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Tom earns 60000\n",
      "Tom is a Dancer\n"
     ]
    }
   ],
   "source": [
    "c.salary(60000)\n",
    "c.artform('Dancer')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "假设在继承一个特定方法的时候，该方法不适合新类。可以通过在新类中用相同的名称再次定义该方法来重写该方法。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 44,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Artist(Person):\n",
    "    def artform(self, job):\n",
    "        self.job = job\n",
    "        print(self.name,\"is a\", self.job)\n",
    "    def salary(self, value):\n",
    "        self.money = value\n",
    "        print(self.name,\"earns\",self.money)\n",
    "        print(\"I am overriding the SoftwareEngineer class's salary method\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 45,
   "metadata": {},
   "outputs": [],
   "source": [
    "c = Artist('Tom',21)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 46,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Tom earns 60000\n",
      "I am overriding the SoftwareEngineer class's salary method\n",
      "Tom is a Dancer\n"
     ]
    }
   ],
   "source": [
    "c.salary(60000)\n",
    "c.artform('Dancer')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "如果输入参数的数量因实例而异，则可以使用星号。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 47,
   "metadata": {},
   "outputs": [],
   "source": [
    "class NotSure:\n",
    "    def __init__(self, *args):\n",
    "        self.data = ' '.join(list(args)) "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {},
   "outputs": [],
   "source": [
    "yz = NotSure('I', 'Do' , 'Not', 'Know', 'What', 'To','Type')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 49,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'I Do Not Know What To Type'"
      ]
     },
     "execution_count": 49,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "yz.data"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 3. 接下来应该怎么做"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "为了学好Python，仅仅看教程是不够的，需要做大量的练习题。可以使用教程里所列的练习题，也可以自己找各个方面的练习题。\n",
    "\n",
    "* 编程比较重要的培养编程思维，如果抄别人写好的代码，发现不了Python的窍门、技巧，因此需要独立自主完成编程练习，也可以给自己出一些小项目，并解决它们。\n",
    "* 你编写的代码越多，你发现的越多，你就越开始欣赏这门语言。\n",
    "* 强烈建议把[《Python作业》](https://gitee.com/pi-lab/machinelearning_homework/blob/master/homework_01_python/README.md)完成\n",
    "* 在完成基本的编程习题之后，可以在[《其他编程练习》](https://gitee.com/pi-lab/machinelearning_homework/blob/master/homework_01_python/README.md#references)里面找一些练习题或者项目做一下。\n",
    "\n",
    "现在已经介绍了Python，可以尝试感兴趣的领域中的不同Python库。强烈建议查看这个Python框架、库和软件列表 http://awesome-python.com\n",
    "\n",
    "\n",
    "Python 教程:\n",
    "* [Python tutorial (廖雪峰）](https://www.liaoxuefeng.com/wiki/1016959663602400)\n",
    "* [Python基础教程](https://www.runoob.com/python/python-tutorial.html)\n",
    "* [Python官方教程（中文版)](https://docs.python.org/zh-cn/3/tutorial/index.html)\n",
    "* [Python官方文档](https://docs.python.org/3/)\n",
    "* [跟海龟学Python](https://gitee.com/pi-lab/python_turtle)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## **最后，享受解决问题的快乐！因为生命短暂，你需要Python!**"
   ]
  }
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