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python类高级话题

2024-07-03 02:00:51   216人阅读

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1、变量名压缩
 
                class 语句内开头 有两个下划线，但结尾没有两个下划线的变量名会自动扩张，从而包含所在类的名称。例如：象spam类内__x这样的变量名会自动变成 _spam__x.原始的变量名会在开头家一个下划线，然后是再加上所在类的类名。这一规则适用了每个开头有两个下划线 的变量名，包括方法名称和实例属性名称。（例如：在spam类内，self.__x实例属性会变成self._spam__x)
 
2、方法是对象：绑定或无绑定
 
                无绑定类方法对象： 无self
 
                                通过对类进行点号运算从而获取函数的属性，会传回无绑定方法对象，调用该方法时，必须提供实例对象作为第一个参数，在python3.0中，一个无绑定方法和一个简单函数相同。可以通过类名来调用，在python2.6中，他是一个特殊的类型，并且不提供一个实例就无法调用
 
                绑定实例方法对象：　self+函数对
 
                                通过对实例进行全运算，从而获取类的汗水属性，会传回绑定方法对象。python在绑定方法对象中自动实现实例和函数的打包，所以不用传递实例去调用该方法。
 
                例如：
 
                class Spam:
 
                                def doit(self,message):
 
                                                print(message)
 
                
 
                在下面代码中，会传回绑定方法对象，把实例（object1）和方法函数(spam.doit)打包起来。我们可以把这个绑定方法赋值给另外一个变量。然后像函数那样进行调用。
 
                object1 = spam()
 
                x = object1.doit
 
                x(‘hello world‘)
 
                另一方面，如果对类进行点号运算来获得doit就会获得无绑定方法对象。也就是函数对象的引用值。要调用这个类方法时，必须传入实例作为最左侧参数
 
                例如：
 
                object2 = Spam()
 
                t = Spam.doit
 
                t(object2,‘howdy‘)
 
                扩展一下：如果我们引用的self属性是引用类中的函数，那么相同的规则也适用于类的方法。self.method表达式是邦定方法，因为self是实例对象。
 
                例如：
 
                class C:
 
                def m1(self,n):
 
                                print(‘m1=‘,n)
 
                def m2(self,t):
 
                                x = self.m1  #这里是通过实例和方法打包，是绑定方法。
 
                                x(t)#在这里调用绑定方法不需要传入实例
 
                                print(‘m2=‘,t)
 
                c = C()
 
                c.m2(88)
 
                print(‘#‘*8)
 
                C.m2(c,77)
 
                print(‘-‘*8)
 
                class B:
 
                                def m1(self,n):
 
                                                print(‘m1=‘,n)
 
                                def m2(self,t):
 
                                                x = B.m1  #这里通过类来获取类中的函数，是无绑定方法对象
 
                                                x(self,t)#这里使用时需要传入一个类对象。
 
                                                print(‘m2=‘,t)
 
                b = B()
 
                B.m2(b,99)
 
                print(‘@‘*8)
 
                b.m2(66)
 
                #输出结果：
 
                m1= 88
 
                m2= 88
 
                ########
 
                m1= 77
 
                m2= 77
 
                --------
 
                m1= 99
 
                m2= 99
 
                @@@@@@@@
 
                m1= 66
 
                m2= 66
 
3、在python3.0中无绑定方法是函数
 
                在python3.0中已经删除"无绑定方法"的概念，但是还是可以使用。在上面介绍的绑定方法，在python3.0中只当作一个简单函数来使用。简单函数不期待传递给他一个实例，非简单函数期待传递一个实例。
 
                此外：在python3.0中不使用一个实例而调用一个方法没有问题，只要这个方法不期待一个实例，并且你通过类调用它而不是通过一个实例调用它。也就是说，只有对通过实例调用，python3.0才会向方法传递一个实例。当通过一个类调用的时候，只有在方法期待一个实例的时候，才必须手动传递一个实例。
 
                class Selfless:
 
                                def __init__(self,data):
 
                                                self.data = data
 
                                def selfless(arg1,arg2):
 
                                                return arg1+arg2
 
                                def normal(self,arg1,arg2):
 
                                                return self.data+arg1+arg2
 
                x = Selfless(2)
 
                print(x.normal(3,4))
 
                print(‘-‘*8)
 
                print(Selfless.normal(x,3,4))
 
                print(‘-‘*8)
 
                print(Selfless.selfless(3,4))  #在python3.0中可以通过一个类去调用这个类的普通方法，但是在python2.6中不行，会抱错。
 
                print(‘-‘*8)
 
                #print(x.selfess(3,4))  不能通过实例去调用一个类的普通方法
 
4、多重集成
 
                在传统类中（默认的类，直到python3.0）,属性搜索处理对所有路径深度优先 ，直到继承树的顶端，然后从左到右
 
                在新式类(以及python.30的所有类中)属性搜索处理沿着树层级，以及更宽广优先的方式。
 
                例如：使用__dict__列出实例属性
 
                class  Listinstance:
 
                                ‘‘‘
 
                                Mix-in class that provides a formatted print() or str() of instance of via inheritance of __str__, coded here:displays instance attrs only;self is the instance of lowest class;
 
                                uses __x names to avoid clashing with client‘s attrs
 
                                ‘‘‘
 
                                def __str__(self):
 
                                                return ‘<Instance of %s, adderss %s:\n%s>‘%(
 
                                                self.__class__.__name__,#每个实例都有一个内置的__class__属性，它引用创建 自己的类，并且每一个类都有一个__name__属性。他引用头部的名称。
 
                                                id(self),  #返回该对象的内存地址
 
                                                self.__attrnames()
 
                                                )
 
                                def __attrnames(self):
 
                                                result = ‘‘
 
                                                for attr in sorted(self.__dict__):
 
                                                                result+=‘\tname %s=%s\n‘%(attr,self.__dict__[attr])
 
                                                return result
 
                s = spam(12)
 
                print(s)
 
                #输出：
 
                                <Instance of spam, adderss 3073187084:
 
                                                name data=12
 
                                >
 
                例如：使用dir列出继承的所有属性
 
                                class ListInherited:
 
                                                ‘‘‘
 
                                                Use dir() to collect both instance attrs and names
 
                                                inherited from its classes; python3.0 shows more
 
                                                names than 2.6 because of the implied object supperclass
 
                                                in the new-style class model; getattr() fetches inherited
 
                                                names not in self.__dict__;use __str__,not __repr__
 
                                                or else this loops when printing bound methods
 
                                                ‘‘‘
 
                                                def __str__(self):
 
                                                                return ‘<Instance of %s, address %s:\n%s>‘(self.__class_.__name,
 
                                                                id(self),
 
                                                                self.__attrnames())
 
                                                def __attrnames(self):
 
                                                                result = ‘‘
 
                                                                for attr in dir(self):
 
                                                                                if attr[:2] == ‘__‘ and attr[-2:] == ‘__‘:
 
                                                                                                result+=‘\tname %s = <>‘%attr
 
                                                                                else:
 
                                                                                                result += ‘\tname %s=%s\n‘%(attr,getattr(self,attr))
 
                                                                return result
 
                例如：列出类树中的每个对象的属性
 
                class ListTree:
 
                                ‘‘‘
 
                                Mix-in that returns an __str__ trace of the entire class
 
                                tree and all its objects‘attrs at and above self;
 
                                run by print(),str() returns constructed string;
 
                                uses __x attr names to void impacting clients;
 
                                uses generator expr to recurse to superclasses;
 
                                uses str.format() to make substituion clear
 
                                ‘‘‘
 
                                def __str__(self):
 
                                                self.__visited = {}
 
                                                return ‘<Instance of {0}, address {1}:\n{2}{3}‘.format(
 
                                                self.__class__.__name__,
 
                                                id(self),
 
                                                self.__attrnames(self,0),
 
                                                self.__listclass(self.__class_,4)
 
                                                )
 
                                def __listclass(self,aClass,indent):
 
                                                dots = ‘.‘*indent
 
                                                if aClass in self.__visited:
 
                                                                return ‘\n{0}<Class {1}:,address {2}:(see above)>\n‘.format(
 
                                                                dots,
 
                                                                aClass.__name,
 
                                                                id(aClass)
 
                                                                )
 
                                                else:
 
                                                                self.__visited[aClass]=True
 
                                                                genabove = (self.__listclass(c,indent+4) for c in aClass.__base__)
 
                                                                return ‘\n{0}<Class {1} , address {2}:\n{3}{4}{5}>\n‘.format(
 
                                                                dots,
 
                                                                aClass.__name__,
 
                                                                id(aClass),
 
                                                                self.__attrnames(aClass,indent),
 
                                                                ‘‘.join(genabove),
 
                                                                dots
 
                                                                )
 
                                def __attrnames(self,obj,indent):
 
                                                spaces = ‘ ‘ * (indent+4)
 
                                                result = ‘‘
 
                                                for attr in sorted(obj.__dict__):
 
                                                                if attr.startwith(‘__‘) and attr.endwith(‘__‘):
 
                                                                                resutl +=spaces +‘{0}=<>\n‘.format(attr)
 
                                                                else:
 
                                                                                result ++space+‘{0}={1}\n‘.format(attr,getattr(obj,attr))
 
                                                return result
 
4、新式类
 
                对于python3.0来说，所有类都是我们所谓的”新式类“，不管他们是否显示继承object.所有类都继承自object.不管显式还是隐式，所有对象都是object的实例
 
                在python2.6及其以前版本，类必须继承自类看作是新式”object，并且获得新式类的特性。
 
5、新式类的变化
 
                1)类和类型合并
 
                                类现在就是类型，并且类型现在就是类，实际上，这二者基本上是同义词。type(I)内置函数返回一个创建这个实例I的类。而不是一个通用实例类型，并且，通常是和I.__class__相同。此外，雷氏type类的实例，type可能子类化
 
6、__slots__
 
                如果一个字类继承一个没有__slots__的超类，那么超类的__dict__属性总是可以访问的，使得字类的__slots__没有意义
 
                如果一个超类定义了一个与超类相同的slots名称，超类slots定义的名称只有通过从直接超类获取其描述符才能访问
 
                由于一个超类__slots__声明的含义受到它出现其中类的限制，所以一个字类将有一个__dict__除非他也声明了一个__slots__
 
                通常从列出实例属性这方面来看，多数类的slots可能需要手动类树爬升、dir用法或者把slot名称当作不同的名称领域的政策
 
7、特性
 
                适用条件是这个类必须继承object
 
                class classic:
 
                                def getx(self)
 
                                                return self.__x
 
                                def setx(self,data):
 
                                                self.__x =data
 
                                def delx(self)
 
                                                self.__x = None
 
                                x = property(getx,setx,delx,None)
 
8、__getattribute__方法只适用于新式类，可以让类拦截所有属性的引用，而不是局限于未定义的引用
 
9、静态方法和类方法
 
                不用一个实例就可以调用 ：静态方法
 
                传递一个类而不是一个实例：类方法
 
10、静态方法和类方法使用实例
 
                静态方法：     
 
                class Spam:
 
                                numInstances = 0
 
                                def __init__(self):
 
                                                Spam.numInstances +=1
 
                                def printNumInstance():
 
                                                print("Number of instance:",Spam.numInstances)
 
                                printNumInstance = staticmethod(printNumInstance)
 
                a = Spam()
 
                b = Spam()
 
                c = Spam()
 
                Spam.printNumInstance()
 
                a.printNumInstance()
 
                继承：
 
                class Sub(Spam):
 
                                def printNumInstance():
 
                                                print(‘extra stauff...‘)
 
                                                Spam.printNumInstance()
 
                                printNumInstance = staticmethod(printNumInstance)
 
                a = Sub()
 
                b = Sub()
 
                a.printNumInstance()
 
                Sub.printNumInstance()
 
                Spam.printNumInstance()
 
                
 
                类方法
 
                class Spam:
 
                                numInstances = 0
 
                                def __init__(self):
 
                                                Spam.numInstances +=1
 
                                def printNumInstance(cls):
 
                                                print("Num of instnace:", cls.numInstances)
 
                                printNumInstance = classmethod(printNumInstance)
 
                a,b = Spam(),Spam()
 
                a.printNumInstance()
 
                Spam.printNumInstance()
 
                继承方法同静态方法相同
 
11、装饰器和元类
 
                例如：
 
                class Spam:
 
                                numInstances = 0
 
                                def __init__(self):
 
                                                Spam.numInstances +=1
 
                                @staticmethod
 
                                def printNumInstance():
 
                                                print("Number of instance:",Spam.numInstances)
 
                a = Spam()
 
                b = Spam()
 
                c = Spam()
 
                Spam.printNumInstance()
 
                a.printNumInstance()

　　


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