A detailed description of attributes, methods, encapsulation, and inheritance based on the Python3 class

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Python class

The classes in Python provide all the basic functions of object-oriented programming: The inheritance mechanism of classes allows for multiple base classes, and derived classes can overwrite any method in the base class, and the method can be called in the base class with the same name.

An object can contain any number and type of data.

Python classes are similar to C + + classes, providing encapsulation, inheritance, multiple inheritance, constructors, and destructors for classes.

In Python3, the top-most parent class of all classes is the object class, similar to Java, and if the class is defined without a parent class, the object class is its immediate parent class.

Class definition

The class definition syntax format is as follows:

Class classname:<statement-1>...<statement-n>

Class object: After a class has been created, it can be accessed through the class name, changed its properties, methods

Instance object: After the class is instantiated, its properties can be used to dynamically add properties (like JavaScript) to the instance object without affecting the class object.

Properties of the class

You can use the dot (.) To access the properties of an object

You can also access properties by using the following functions:

GetAttr (obj, name[, default]): Accessing the properties of an object

Hasattr (obj,name): Checks if a property exists

SetAttr (Obj,name,value): Sets a property. If the property does not exist, a new property is created

Delattr (obj, name): Delete attribute

Python built-in class properties

__DICT__: Properties of the Class (contains a dictionary, consisting of the data properties of the Class)

__DOC__: Document string for Class

__NAME__: Class name

__MODULE__: The module where the class definition resides (the full name of the class is ' __main__.classname ', if the class is in an import module mymod, then classname.__module__ equals Mymod)

__BASES__: All parent classes of a class make up elements (containing a tuple of all the parent classes)

Class Person: The "Person class" Def __init__ (self, name, age, gender): print (' Enter the initialization of person ') Self.name = name Self.age = Age Self.gender = Gender print (' Initialize of person left ') def getName (self): print (self.name) p = person (' ice ', 18, ' male ') pr int (p.name) # iceprint (p.age) # 18print (p.gender) # Man print (Hasattr (p, ' weight ')) # false# Add weight attribute to P p.weight = ' 70kg ' pri NT (Hasattr (p, ' weight ')) # Trueprint (GetAttr (p, ' name ')) # Iceprint (p.__dict__) # {' Age ': ' Gender ': ' Male ', ' name ': ' Ice ' }print (person.__name__) # personprint (person.__doc__) # Person class print (person.__dict__) # {' __doc__ ': ' Person class ', ' __ weakref__ ': <attribute ' __weakref__ ' of ' person ' objects>, ' __init__ ': <function person.__init__ at 0x000000000284e950>, ' getName ': <function person.getname at 0x000000000284ea60>, ' __dict__ ': <attribute ' _ _dict__ ' of ' person ' objects>, ' __module__ ': ' __main__ '}print (person.__mro__) # (<class ' __main__. Person ', <class ' object ' > ' Print (person.__bases__) # (<Class ' object ',) print (person.__module__) # __main__ 

Methods of the class

Inside the class, using the DEF keyword, you can define a method for a class that differs from a generic function definition, and that the class method must contain the parameter self, which is the first argument.

The proprietary methods of the class:

The __init__ constructor, which is called when the object is generated

__del__ destructors, using when releasing objects

__repr__ Printing, converting

__setitem__ Assignment by index

__getitem__ getting values by index

__len__ Get length

__CMP__ comparison operations

__call__ function call

__add__ Plus arithmetic

__SUB__ Reduction Operations

__mul__ Multiply operation

__P__ in addition to operations

__mod__ Calculating the remainder

__pow__ said Fang

The __init__ () method is a special method, called a constructor or initialization method of a class, that is called when an instance of the class is created, similar to a constructor in C + +. Just rewrite the __init__ () method in your custom class.

Class Person:  def __init__ (self, name, age, gender):    print (' Enter person initialization ')    self.name = name    Self.age = Age    Self.gender = gender    print (' Initialize of person left ')  def getName (self):    print (self.name) # Person instance Object P = Person (' ice ', 18, ' Man ') print (p.name) print (p.age) print (P.gender) p.getname () # Enter the person's initialization # leave the person's initialization # ice# 18# Man # Ice

destructor __del__, __del__ is called when the object dies, and the __del__ method runs when the object is no longer being used:

Method

Instance method: can only be called through an instance, the first parameter defined by the instance method can only be referenced by the instance itself

Class Myclass:  def foo (self):    print ("Self", ' foo ') A=myclass () #既然是实例对象, then create Instance A.foo () #输出类里的函数地址print ( ID (a)) #输出类对象的地址 # The same as the result address

Class method: Defines a class method, to use the adorner @classmethod, the first parameter defined is a reference to the class object, which can be used directly from a class or instance

Class Myclass: @classmethod # class Decorator  def foo2 (CLS):    Print (ID (CLS), ' Foo2 ')  #类对象, can be called directly, no need to instantiate print (ID ( Myclass), ' yy ') Myclass.foo2 () #直接可以调用

Static methods: Define static methods using adorner @staticmethod, no default mandatory parameters, direct call through class and instance

Class Myclass: @staticmethod # static method  def Foo3 ():    print (' Foo3 ') Myclass.foo3 () #没有参数a. Foo3 () #结果foo3

Encapsulation of classes

Python distinguishes the access rights of properties and methods by naming them by variable names, which are equivalent to public in C + + and Java

The private property of the class: __private_attrs: Two underscores, declares that the property is private and cannot be used outside of the class or accessed directly. Self.__private_attrs when used in methods inside a class.

Private method of the class: __private_method: Two underscore, declares that the method is a private method and cannot be called outside of a class. Calling Self.__private_methods inside a class

Although Python does not allow instantiated classes to access private data, you can use Object._classname__attrname to access properties. In fact, the implementation of Python's internal privatization only changed the Attrname attribute to _classname__attrname.

Class Demo:  __id = 123456  def getId (self):    return self.__idtemp = Demo () # Print (temp.__id) # error Attributeerro R: ' Demo ' object has no attribute ' __id ' Print (Temp.getid ()) # 123456print (temp._demo__id) # 123456

Inheritance of Classes

One of the main benefits of object-oriented programming is the reuse of code, and one way to implement this reuse is through inheritance mechanisms. Inheritance can be fully understood as a type and subtype relationship between classes.

What to note: Inherit the syntax class derived class name (base class name)://... The base class name is written in parentheses, and the base class is specified in the tuple at the time the class is defined.

Some of the characteristics of inheritance in Python:

1: The construction of the base class in inheritance (The __init__ () method) is not automatically called, it needs to be called specifically in the construction of its derived class. Use Super (). __init__ () or parentclassname.__init__ ()

2: When calling a method of the base class, you need to prefix the class name of the base class with the Self argument variable. Unlike calling a normal function in a class, you do not need to take the self argument

3:python always looks for a method of the corresponding type first, and if it cannot find the corresponding method in the derived class, it begins to look in the base class one by one. (Find the method that was called in this class before you can find it in the base class).

If more than one class is listed in an inheritance tuple, it is called "Multiple inheritance."

Grammar:

The declarations of derived classes are similar to their parent classes, and the list of inherited base classes follows the class name.

Polymorphic

If the functionality of the parent method does not meet the requirements, you can override the parent class's methods in the subclass. An overridden method that invokes its corresponding subclass when the instance object invokes the method

python3.3 class and inheritance small case

The classes in Hon provide all the basic functions of object-oriented programming: The inheritance mechanism of classes allows for multiple base classes, and derived classes can overwrite any method in the base class, and the method can be called in the base class with the same name.

Class Base:  def __init__ (self):    self.data=[]  def Add (self,x):    self.data.append (x)  def addtwice (self,x):    self.add (x)    Self.add (x) # Child extends BaseClass child (Base):  def Plus (self,a,b):    Return A+bochild=child () ochild.add ("str1") Ochild.add (999) ochild.addtwice (4) print (ochild.data) print (Ochild.plus ( 2, 3))

An object can contain any number and type of data.

Python classes are similar to C + + classes, providing encapsulation, inheritance, multiple inheritance, constructors, and destructors for classes.

In Python3, the top-most parent class of all classes is the object class, similar to Java, and if the class is defined without a parent class, the object class is its immediate parent class.

Class definition

The class definition syntax format is as follows:

Class classname:<statement-1>...<statement-n>

Class object: After a class has been created, it can be accessed through the class name, changed its properties, methods

Instance object: After the class is instantiated, its properties can be used to dynamically add properties (like JavaScript) to the instance object without affecting the class object.

Properties of the class

You can use the dot (.) To access the properties of an object

You can also access properties by using the following functions:

GetAttr (obj, name[, default]): Accessing the properties of an object

Hasattr (obj,name): Checks if a property exists
SetAttr (Obj,name,value): Sets a property. If the property does not exist, a new property is created

Delattr (obj, name): Delete attribute

Python built-in class properties

__DICT__: Properties of the Class (contains a dictionary, consisting of the data properties of the Class)

__DOC__: Document string for Class

__NAME__: Class name

__MODULE__: The module where the class definition resides (the full name of the class is ' __main__.classname ', if the class is in an import module mymod, then classname.__module__ equals Mymod)

__BASES__: All parent classes of a class make up elements (containing a tuple of all the parent classes)

Class Person: The "Person class" Def __init__ (self, name, age, gender): print (' Enter the initialization of person ') Self.name = name Self.age = Age Self.gender = Gender print (' Initialize of person left ') def getName (self): print (self.name) p = person (' ice ', 18, ' male ') pr int (p.name) # iceprint (p.age) # 18print (p.gender) # Man print (Hasattr (p, ' weight ')) # false# Add weight attribute to P p.weight = ' 70kg ' pri NT (Hasattr (p, ' weight ')) # Trueprint (GetAttr (p, ' name ')) # Iceprint (p.__dict__) # {' Age ': ' Gender ': ' Male ', ' name ': ' Ice ' }print (person.__name__) # personprint (person.__doc__) # Person class print (person.__dict__) # {' __doc__ ': ' Person class ', ' __ weakref__ ': <attribute ' __weakref__ ' of ' person ' objects>, ' __init__ ': <function person.__init__ at 0x000000000284e950>, ' getName ': <function person.getname at 0x000000000284ea60>, ' __dict__ ': <attribute ' _ _dict__ ' of ' person ' objects>, ' __module__ ': ' __main__ '}print (person.__mro__) # (<class ' __main__. Person ', <class ' object ' > ' Print (person.__bases__) # (<Class ' object ',) print (person.__module__) # __main__ 

Methods of the class

Inside the class, using the DEF keyword, you can define a method for a class that differs from a generic function definition, and that the class method must contain the parameter self, which is the first argument.

The proprietary methods of the class:

The __init__ constructor, which is called when the object is generated

__del__ destructors, using when releasing objects

__repr__ Printing, converting

__setitem__ Assignment by index

__getitem__ getting values by index

__len__ Get length

__CMP__ comparison operations

__call__ function call

__add__ Plus arithmetic

__SUB__ Reduction Operations

__mul__ Multiply operation

__P__ in addition to operations

__mod__ Calculating the remainder

__pow__ said Fang

The __init__ () method is a special method, called a constructor or initialization method of a class, that is called when an instance of the class is created, similar to a constructor in C + +. Just rewrite the __init__ () method in your custom class.

Class Person:  def __init__ (self, name, age, gender):    print (' Enter person initialization ')    self.name = name    Self.age = Age    Self.gender = gender    print (' Initialize of person left ')  def getName (self):    print (self.name) # Person instance Object P = Person (' ice ', 18, ' Man ') print (p.name) print (p.age) print (P.gender) p.getname () # Enter the person's initialization # leave the person's initialization # ice# 18# Man # Ice

destructor __del__, __del__ is called when the object dies, and the __del__ method runs when the object is no longer being used:

Encapsulation of classes

Python distinguishes the access rights of properties and methods by naming them by variable names, which are equivalent to public in C + + and Java

The private property of the class: __private_attrs: Two underscores, declares that the property is private and cannot be used outside of the class or accessed directly. Self.__private_attrs when used in methods inside a class.

Private method of the class: __private_method: Two underscore, declares that the method is a private method and cannot be called outside of a class. Calling Self.__private_methods inside a class

Although Python does not allow instantiated classes to access private data, you can use Object._classname__attrname to access properties. In fact, the implementation of Python's internal privatization only changed the Attrname attribute to _classname__attrname.

Class Demo:  __id = 123456  def getId (self):    return self.__idtemp = Demo () # Print (temp.__id) # error Attributeerro R: ' Demo ' object has no attribute ' __id ' Print (Temp.getid ()) # 123456print (temp._demo__id) # 123456

Inheritance of Classes

One of the main benefits of object-oriented programming is the reuse of code, and one way to implement this reuse is through inheritance mechanisms. Inheritance can be fully understood as a type and subtype relationship between classes.

What to note: Inherit the syntax class derived class name (base class name)://... The base class name is written in parentheses, and the base class is specified in the tuple at the time the class is defined.

Some of the characteristics of inheritance in Python:

1: The construction of the base class in inheritance (The __init__ () method) is not automatically called, it needs to be called specifically in the construction of its derived class. Use Super (). __init__ () or parentclassname.__init__ ()

2: When calling a method of the base class, you need to prefix the class name of the base class with the Self argument variable. Unlike calling a normal function in a class, you do not need to take the self argument

3:python always looks for a method of the corresponding type first, and if it cannot find the corresponding method in the derived class, it begins to look in the base class one by one. (Find the method that was called in this class before you can find it in the base class).

If more than one class is listed in an inheritance tuple, it is called "Multiple inheritance."

Grammar:

The declarations of derived classes are similar to their parent classes, and the list of inherited base classes follows the class name.

Polymorphic

If the functionality of the parent method does not meet the requirements, you can override the parent class's methods in the subclass. An overridden method that invokes its corresponding subclass when the instance object invokes the method

python3.3 class and inheritance small case

Class Base:def __init__ (self): self.data=[]def Add (self,x): Self.data.append (x) def addtwice (self,x): Self.add (x) Self.add (x) # Child extends BaseClass child (Base):d EF Plus (self,a,b): Return A+bochild=child () ochild.add ("str1") Ochild.add (999) ochild.addtwice (4) print (ochild.data) print (Ochild.plus (2,3))