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"# 编程入门11：Python面向对象\n",
"你已经知道在Python中“一切皆对象”，每个对象都有特定的类型，现在让我们来尝试创建自己的类型——这需要使用class关键字来定义新的“类”（Class），类是用来生成对象的“模板”，对象则是其所属类的“实例”——以下是在交互模式中自定义Thing类，并调用其默认构造器生成一个Thing类的实例对象（注意：自定义类的命名规范要求单词首字母大写）：\n",
"```\n",
"In [1]: class Thing:\n",
" ...: \"\"\"最简单的自定义类\"\"\"\n",
" ...: \n",
"\n",
"In [2]: type(Thing)\n",
"Out[2]: type\n",
"\n",
"In [3]: t = Thing()\n",
"\n",
"In [4]: type(t)\n",
"Out[4]: __main__.Thing\n",
"```\n",
"你可以看到，Thing对象属于type类型，是type类的一个实例；t对象属于Thing类型，是Thing类的一个实例——当你在程序中定义自己的类来生成实例对象，就算是“面向对象编程”（Object-Oriented Programming，简称OOP）。面向对象的编程方式使用类来模拟和组织现实世界的事物，可以令程序结构更灵活、条理更清晰。\n",
"\n",
"\n",
"上面定义的Thing类所生成的实例对象并不能做什么事情，让我们再来创建一个包含了具体子语句的“船”类并生成两个“船”对象：\n",
"```\n",
"In [5]: class Ship:\n",
" ...: \"\"\"船类\"\"\"\n",
" ...: def __init__(self, name=None):\n",
" ...: \"\"\"初始化船实例\"\"\"\n",
" ...: self.name = name # 船名\n",
" ...: self.crew = 0 # 船员人数\n",
" ...: def join(self, number):\n",
" ...: \"\"\"船员加入\"\"\"\n",
" ...: self.crew += number\n",
" ...: return self.crew\n",
" ...: \n",
"\n",
"In [6]: s1 = Ship(\"郑和\")\n",
"\n",
"In [7]: s1.crew = 200\n",
"\n",
"In [8]: s2 = Ship(\"戚继光\")\n",
"\n",
"In [9]: s2.join(100)\n",
"Out[9]: 100\n",
"\n",
"In [10]: s2.crew\n",
"Out[10]: 100\n",
"```\n",
"Ship类定义了一个特殊的“初始化”方法```__init__```，这样就能在调用构造器生成实例时加入新的实例“属性”（Property），所谓实例属性就是实例对象的“成员变量”，例如Ship类的实例增加了name和crew属性——从现实概念来理解，任何船都有船名和船员人数这两个数据，但每艘船又有各自的具体数据值。实例属性和实例方法是最常见的两种类成员，Python规定特殊类成员名以两个下划线开始和结束，其他类成员名遵循标准的变量命名规范，注意这里有一个细节概念：作为类成员的```__init__```属于函数，作为实例成员的```__init__```则属于方法，在类中定义函数时约定首个参数为“self”，它会指向所生成的实例对象以便操作其成员，对应的实例方法则无此参数，所以调用Ship构造器时只需传入一个参数（也可以不传入任何参数，因为name指定了默认值）。除了实例属性，你也可以定义新的实例方法，让实例能够做更多的事情——例如“船”类还有一个“船员加入”方法。\n",
"```\n",
"In [11]: help(Ship)\n",
"Help on class Ship in module __main__:\n",
"\n",
"class Ship(builtins.object)\n",
" | 船类\n",
" | \n",
" | Methods defined here:\n",
" | \n",
" | __init__(self, name=None)\n",
" | 初始化船实例\n",
" | \n",
" | join(self, number)\n",
" | 船员加入\n",
" | \n",
" | ----------------------------------------------------------------------\n",
" | Data descriptors defined here:\n",
" | \n",
" | __dict__\n",
" | dictionary for instance variables (if defined)\n",
" | \n",
" | __weakref__\n",
" | list of weak references to the object (if defined)\n",
"\n",
"\n",
"In [12]: type(Ship.__init__)\n",
"Out[12]: function\n",
"\n",
"In [13]: type(s2.__init__)\n",
"Out[13]: method\n",
"\n",
"In [14]: s1.__dict__\n",
"Out[14]: {'crew': 200, 'name': '郑和'}\n",
"```\n",
"实例对象之所以拥有不必自定义而默认存在的特殊成员，是因为面向对象编程的一个重要特性“继承”（Inheritance）——使用继承机制能够将复杂的系统有机地组织起来，所有类都是同一个庞大家族的成员——定义类时可以在类名后加括号指定“基类”，新类将成为其“子类”；如果不指定基类，就默认为最基本的“object”类的子类。子类会继承基类的现有成员，子类定义属性和方法时如果与基类成员同名，就会“覆盖”基类成员。例如下面的程序定义了“船”类及其子类“战舰”类：\n",
"```\n",
"\"\"\"ship.py 船的家族\"\"\"\n",
"\n",
"\n",
"class Ship:\n",
" \"\"\"船类\"\"\"\n",
" def __init__(self, name=None):\n",
" \"\"\"初始化船实例\"\"\"\n",
" self.name = name # 船名\n",
" self.crew = 0 # 船员人数\n",
"\n",
" def join(self, number):\n",
" \"\"\"船员加入\"\"\"\n",
" self.crew += number\n",
" return self.crew\n",
"\n",
"\n",
"class Warship(Ship):\n",
" \"\"\"战舰类\"\"\"\n",
" def __init__(self, name=None, level=None):\n",
" super().__init__(name) # 先调用基类初始化方法\n",
" self.level = level # 舰级\n",
"\n",
"\n",
"if __name__ == \"__main__\":\n",
" ws1 = Warship(\"蓝色空间\", \"恒星级\")\n",
" ws1.join(500)\n",
" print(\"{}战舰{}号，现有舰员{}人。\".format(ws1.level, ws1.name, ws1.crew))\n",
"```\n",
"你可以注意到Warship类重新定义了```__init__```，这就会覆盖Ship类中的```__init__```，所以先调用基类的```__init__```才能继承到基类定义的实例属性name和crew。\n",
"\n",
"接下来的示例是一个简单的计算器：\n",
"```\n",
"\"\"\"tkcalc.pyw 简单的计算器\n",
"\"\"\"\n",
"import tkinter as tk\n",
"\n",
"\n",
"class Calc(tk.Tk):\n",
" \"\"\"计算器窗体类\"\"\"\n",
" def __init__(self):\n",
" \"\"\"初始化实例\"\"\"\n",
" tk.Tk.__init__(self)\n",
" self.title(\"计算器\")\n",
" self.memory = 0 # 暂存数值\n",
" self.create()\n",
"\n",
" def create(self):\n",
" \"\"\"创建界面\"\"\"\n",
" btn_list = [\"C\", \"M->\", \"->M\", \"/\",\n",
" \"7\", \"8\", \"9\", \"*\",\n",
" \"4\", \"5\", \"6\", \"-\",\n",
" \"1\", \"2\", \"3\", \"+\",\n",
" \"+/-\", \"0\", \".\", \"=\"]\n",
" r = 1\n",
" c = 0\n",
" for b in btn_list:\n",
" self.button = tk.Button(self, text=b, width=5,\n",
" command=(lambda x=b: self.click(x)))\n",
" self.button.grid(row=r, column=c, padx=3, pady=6)\n",
" c += 1\n",
" if c > 3:\n",
" c = 0\n",
" r += 1\n",
" self.entry = tk.Entry(self, width=24, borderwidth=2,\n",
" bg=\"yellow\", font=(\"Consolas\", 12))\n",
" self.entry.grid(row=0, column=0, columnspan=4, padx=8, pady=6)\n",
"\n",
" def click(self, key):\n",
" \"\"\"响应按钮\"\"\"\n",
" if key == \"=\": # 输出结果\n",
" result = eval(self.entry.get())\n",
" self.entry.insert(tk.END, \" = \" + str(result))\n",
" elif key == \"C\": # 清空输入框\n",
" self.entry.delete(0, tk.END)\n",
" elif key == \"->M\": # 存入数值\n",
" self.memory = self.entry.get()\n",
" if \"=\" in self.memory:\n",
" ix = self.memory.find(\"=\")\n",
" self.memory = self.memory[ix + 2:]\n",
" self.title(\"M=\" + self.memory)\n",
" elif key == \"M->\": # 取出数值\n",
" if self.memory:\n",
" self.entry.insert(tk.END, self.memory)\n",
" elif key == \"+/-\": # 正负翻转\n",
" if \"=\" in self.entry.get():\n",
" self.entry.delete(0, tk.END)\n",
" elif self.entry.get()[0] == \"-\":\n",
" self.entry.delete(0)\n",
" else:\n",
" self.entry.insert(0, \"-\")\n",
" else: # 其他键\n",
" if \"=\" in self.entry.get():\n",
" self.entry.delete(0, tk.END)\n",
" self.entry.insert(tk.END, key)\n",
"\n",
"\n",
"if __name__ == \"__main__\":\n",
" Calc().mainloop()\n",
"```\n",
"\n",
"\n",
"程序窗体继承自tkinter.Tk类，要加部件就定义实例属性，要做事情就使用实例方法，这就是OOP的方式。\n",
"\n",
"——编程原来这样……\n",
"\n",
"## 编程小提示\n",
"这次给大家分享的是“Python资源大全中文版”，好用的东西都在其中了……\n",
"https://github.com/jobbole/awesome-python-cn\n",
"\n",
"下一篇：[编程入门12：Python异常处理](12_except.ipynb)"
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