1 Method is not overloaded
Python in , The parameter of the method does not declare a type （ Determine the type of parameter when calling ）, The number of parameters can also be determined by
Variable parameter control . therefore ,Python There is no method overload in . Defining a method can be called in many ways ,
It is equivalent to implementing the overloading of methods in other languages .
2. The dynamics of methods
Python It's dynamic language , We can dynamically add new methods to classes , Or dynamically modify the existing methods of the class .
3. Private properties and private methods ( Implement encapsulation )
Python There are no strict access control restrictions on class members , This is different from other object-oriented languages . About private ownership
Properties and private methods , There are the following points ：
1. Usually we agree , Attributes starting with two underscores are private (private). Others are public (public).
2. Class can access private properties ( Method )
3. Private properties cannot be accessed directly outside the class ( Method )
4. Class can be passed “_ Class name __ Private property ( Method ) name ” Access private properties ( Method )
【 notes 】 Methods are essentially properties ！ It's just that you can pass () Just execution
[email protected] Decorator
@property You can change the calling mode of a method into “ Calling a ”.
5. Attribute and method naming summary
· _xxx： Protection member , Out-of-service “from module import * ” Import , Only class objects and subclass objects can access
Ask these members .
· __xxx__： Special members of the system definition
· __xxx： Private members in class , Only class objects can access , Subclass objects are also inaccessible .（ but , Out of class
The ministry can go through “ Object name . _ Class name __xxx” This special way to access .Python There are no strictly private members ）
notes ： Methods and properties follow the above rules .
6 Class coding style
1. Class names are capitalized , Use the hump principle between multiple words .
2. Instance name 、 The module name is in lowercase , Multiple words are separated by underscores .
3. Each class , Should follow “ docstring ”, Explain the function of this class .
4. You can organize code with blank lines , But don't abuse . In class , Use a blank line separation method ; Module , Use two
Empty lines separate multiple classes
7 Three characteristics of object orientation ： Inherit 、 encapsulation （ hide ）、 polymorphic
7.1 encapsulation （ hide ）
Hide object properties and implementation details , Only provide necessary methods for external . Is equivalent to “ The details are encapsulated ”, only
External exposure “ Related call methods ”.
7.2 · Inherit
Inheritance can make subclasses have the characteristics of their parents , Improved code reuse .
Python Support for multiple inheritance , A subclass can inherit more than one parent class . The inherited syntax format is as follows ：
class Subclass class name ( Parent class 1[, Parent class 2,...])：
The class body
If no parent class is specified in the class definition , The default parent class is object class .
When you define subclasses , The constructor of the parent class must be called in its constructor . The call format is as follows ：
Parent class name .__init__(self, parameter list )
7.2.1 Inheritance and overriding of class members
1. Members inherit ： The subclass inherits all members of the parent class except the constructor .
2. Method rewriting ： Subclasses can redefine the methods in the parent class , This will override the methods of the parent class , Also known as “ rewrite
7.2.2 View the inheritance hierarchy of the class
Through the method of class mro() Or class properties __mro__ You can output the inheritance hierarchy of this class .
7.2.3 object The root class
object Class is the parent of all classes .
7.2.4 dir() View object properties
Built in functions dir(), It allows us to easily see all the properties of the specified object .
7.2.5 rewrite __str__() Method
object There is one __str__() Method , Used to return a for “ Description of the object ”, Corresponds to the built-in function str()
Often used for print() Method , Help us view the information of the object .__str__() Can be rewritten .
7.2.6 multiple inheritance
Python Support for multiple inheritance , A subclass can have multiple “ Immediate parents ”. such , You have “ Multiple fathers
class ” Characteristics . But because of , This will be “ The overall hierarchy of the class ” It's very complicated , Avoid using .
7.2.7 MRO()
Python Support for multiple inheritance , If there are methods with the same name in the parent class , When the subclass does not specify the parent class name , The interpreter will
“ From left to right ” Search in order .
MRO（Method Resolution Order）： Method parsing order . We can go through mro() Methods to get
“ Class hierarchy ”, The method parsing order is also according to this “ Class hierarchy ” Looking for .
7.2.8 super() Get the parent class definition
In a subclass , If you want to get the method of the parent class , We can go through super() To do it .super() Represents the definition of the parent class , Not a parent object .
7.3 polymorphic
Polymorphism means that the same method call will produce different behavior due to different objects .
Note the following about polymorphism 2 spot ：
1. Polymorphism is the polymorphism of method , Property is not polymorphic .
2. The existence of polymorphism has 2 Necessary conditions ： Inherit 、 Method rewriting .
7.4 Special methods and operator overloads
Python The operator of is actually implemented by calling a special method of the object .
7.5 Shallow and deep copies of objects
· Assignment of variables
Just form two variables , It actually points to the same object .
· Shallow copy
Python Copies are generally shallow copies . When copying , The contents of sub objects contained in the object are not copied . therefore , Source object
And the copy object will reference the same child object .
· Deep copy
Use copy Modular deepcopy function , Recursively copies the child objects contained in the object . Source and copy objects
All child objects are also different .
7.6 Combine
“is-a” Relationship , We can use “ Inherit ”. So as to realize the methods and properties of the parent class owned by the child class .“is-a”
Relationship refers to a relationship like this ： Dogs are animals ,dog is animal. Dogs should inherit animals .
“has-a” Relationship , We can use “ Combine ”, You can also implement that one class has methods and properties of another class .”
has-a” Relationship refers to such a relationship ： Cell phones have CPU. MobilePhone has a CPU.
7.7 Design patterns _ Factory mode implementation
Design pattern is a special content of object-oriented language , It is our fixed practice when facing a certain kind of problem , Design
There are many patterns , What's more popular is ：GOF（Goup Of Four）23 Design patterns .
The two most common patterns for beginners ： Factory mode and singleton mode
7.8 Design patterns _ Singleton mode implementation
The singleton pattern （Singleton Pattern） The core role of is to ensure that a class has only one instance , And provide a
Global access points to access this instance .
Singleton mode generates only one instance object , Reduce the overhead of system resources . When an object is generated, it needs to compare
More resources , Such as reading configuration file 、 When other dependent objects are generated , Can produce a “ Singleton object ”, And then forever
Resident in memory , Thus greatly reducing the overhead .
