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Class	类

类

类提供了将数据和功能捆绑在一起的方法。创建新类会创建一种新类型的对象，从而允许创建该类型的新实例。每个类实例都可以附加属性以维护其状态。类实例还可以具有用于修改其状态的方法（由其类定义）。

与其他编程语言相比，Python的类机制添加的类最少新的语法和语义。它是C ++中的类机制的混合体。 Python类提供面向对象编程的所有标准功能：类继承机制允许多个基类，派生类可以覆盖其基类或类的任何方法，并且方法可以调用具有相同名称的基类的方法。对象可以包含任意数量和种类的数据。与模块一样，类也参与Python的动态特性：它们是在运行时创建的，可以在创建后进一步修改。

类定义语法：

最简单的类定义形式如下所示：

class ClassName: 
    <statement-1> 
        ... 
        ... 
        ... 
    <statement-N>

Class Objects:

Class objects support two kinds of operations: attribute references and instantiation.

Attribute references use the standard syntax used for all attribute references in Python: obj.name. Valid attribute names are all the names that were in the class's namespace when the class object was created. So, if the class definition looked like this:


蟒蛇 class MyClass： “”一个简单的示例类“”“ 我= 12345

def f(self): return 'hello world'

Then MyClass.i and MyClass.f are valid attribute references, returning an integer and a function object, respectively. Class attributes can also be assigned to, so you can change the value of MyClass.i by assignment. __doc__ is also a valid attribute, returning the docstring belonging to the class: "A simple example class".

Class instantiation uses function notation. Just pretend that the class object is a parameterless function that returns a new instance of the class. For example (assuming the above class):


蟒蛇 x = MyClass（）

Creates a new instance of the class and assigns this object to the local variable x.

The instantiation operation (“calling” a class object) creates an empty object. Many classes like to create objects with instances customized to a specific initial state. Therefore a class may define a special method named init(), like this:


蟒蛇 def **init** （self）： self.data = \[\]

When a class defines an __init__() method, class instantiation automatically invokes __init__() for the newly-created class instance. So in this example, a new, initialized instance can be obtained by:


蟒蛇 x = MyClass（）

Of course, the __init__() method may have arguments for greater flexibility. In that case, arguments given to the class instantiation operator are passed on to __init__(). For example,


蟒蛇 类复杂： def **init** （self，realpart，imagpart）： self.r = realpart self.i = imagpart ...

x =复数（3.0，-4.5）

> > > xr，xi （3.0，-4.5） \`\`\`

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类

类定义语法：

Class Objects:

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