【Python object-oriented 】

• Create a class

class Employee:
' Base class for all employees '
empCount = 0
def __init__(self, name, salary):
self.name = name
self.salary = salary
Employee.empCount += 1
def displayCount(self):
print "Total Employee %d" % Employee.empCount
def displayEmployee(self):
print "Name : ", self.name, ", Salary: ", self.salary

empCount Variable is a class variable , Its value will be shared among all instances of this class . You can use it in internal or external classes Employee.empCount visit .

The first method __init__() Method is a special method , A constructor or initialization method called a class , This method is called when an instance of this class is created

self Represents an instance of a class ,self Required when defining methods of a class , Although it is not necessary to pass in the corresponding parameters when calling .（self Represents an instance of a class , Not class ）

• Create instance object
  

Key words are commonly used in other programming languages of instantiation classes new, But in Python There is no such keyword in , Class instantiation is similar to function call .

The following uses the name of the class Employee To instantiate , And pass __init__ Method receive parameters .

emp1 = Employee("Zara", 2000)

• add to , Delete , Modify the properties of a class
  

emp1.age = 7 # Add one 'age' attribute
emp1.age = 8 # modify 'age' attribute
del emp1.age # Delete 'age' attribute 

• Python Built in class properties
  

__dict__ : Attributes of a class （ Include a dictionary , Consists of data properties of a class ）
__doc__ : Document string for class
__name__: Class name
__module__: Module of class definition （ The full name of the class is '__main__.className', If the class is in an import module mymod in , that className.__module__ be equal to mymod）

__bases__ : All parent elements of a class （ Contains a tuple of all parent classes ）

• python Destruction of objects ( Garbage collection )
  

Python The simple technique of reference counting is used to track and recycle garbage .

An internal tracking variable , Called a reference counter .

When the object is created , You create a reference count , When this object is no longer needed , in other words , The reference count for this object changes to 0 when , It's recycled . But recycling is not " immediately " Of , By the interpreter at the right time , Reclaim the memory space occupied by garbage objects .

Python The garbage collector of is actually a reference counter and a circular garbage collector . As a complement to the reference count , The garbage collector will also notice that the total amount allocated is very large （ And those not destroyed by reference counting ） The object of . under these circumstances , The interpreter will pause , Trying to clean up all unreferenced loops .

Destructor __del__ ,__del__ Called when the object is destroyed , When the object is no longer in use ,__del__ Method run

• Class inheritance

class Derived class name ( Base class name )
...

If the construction method of the parent class is needed in the child class, it needs to display the construction method of calling the parent class , Or do not override the constructor of the parent class .

When a method of a base class is called , Need to prefix the class name of the base class , And you need to bring it self Parameter variable . The difference is that it is not necessary to bring the ordinary function into the class self Parameters .

• Method rewriting
  
• Operator overloading
  

#!/usr/bin/python
class Vector:
def __init__(self, a, b):
self.a = a
self.b = b
def __str__(self):
return 'Vector (%d, %d)' % (self.a, self.b)
def __add__(self,other):
return Vector(self.a + other.a, self.b + other.b)
v1 = Vector(2,10)
v2 = Vector(5,-2)
print v1 + v2

• Class properties and methods
  

Private properties of class ：__private_attrs： Start with two underscores , Declare the property private , Can't be used outside of the class or accessed directly . When used in methods within a class self.__private_attrs.

Private method of class ：__private_method： Start with two underscores , Declare the method private , Cannot call... Outside of a class . Called inside a class self.__private_methods

notes ：Python Instantiated classes are not allowed to access private data , But you can use object._className__attrName（ Object name ._ Class name __ Private property name ） Access properties

• Underline 、 Double underline 、 Double underline description
  

__foo__: It's defined as a special method , Generally, the system defines the name , similar __init__() And so on. .

_foo: What begins with a single underscore is protected Variable of type , That is, the protection type can only be accessed by itself and its subclass , Cannot be used for from module import *

__foo: Double underscores indicate private types (private) The variable of , Only the class itself can be allowed to access .

• Python Why inherit object class ？
  

Inherit object Class is a new class , No inheritance object Class is a classic class , stay Python 2.7 There will be differences between the new class and the classic class in terms of multiple inheritance ：

Classic class ：Python Will search the required method according to the depth first method .

The new class ：Python Will search the required method according to the breadth first method .