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One and two major programming ideas

II. Classes and objects

A simple example:

Everything in python is an object. Here is an opening picture:

Define classes in Python

Example 1:

Class Student: passprint (id (Student)) # 1149225945800print (type (Student)) # print (Student) #

Example 2:

Class Student: native_place=' Jilin'# Class attribute def _ _ init__ (self,name Age): self.name=name self.age=age # instance method def eat (self): print ("students are eating") # static method @ staticmethod def method (): print ("I am a static method") # class method @ classmethod def cm (cls): print ("I am a class method") IV. Object creation

Example 1:

# instance object student1=Student ("Zhang San", 18) print (student1) print (id (student1)) print (type (student1)) print ("- -") # object, representing the class print (Student) print (id (Student)) print (type (Student))

Example 2:

# instance object student1=Student ("Zhang San", 18) print (student1.name) print (student1.age) # instance method calls have the following two uses: print (student1.eat ()) print (Student.eat (student1)) 5. Class properties, class methods, static methods

Example 1: class attributes

# Class attribute student1=Student ("Zhang San", 18) student2=Student ("Li Si" 19) print (Student.native_place) # Jilin print (student1.native_place) # Jilin print (student2.native_place) # Jilin Student.native_place=' Sichuan 'print (student1.native_place) # Sichuan print (student2.native_place) # Sichuan #-- -student1.native_place=' Guangdong 'print (student1.native_place) # Guangdong print (student2.native_place) # Sichuan

Example 2: class method, static method

# Class methods, static methods use student1=Student ("Zhang San", 18) Student.method () # I am static method Student.cm () # I am class method VI, dynamic binding properties and methods

Python is a dynamic language. After creating an object, you can dynamically bind properties and methods.

For example: attribute binding

Class Student: def _ init__ (self,name,age): self.name=name self.age=age # instance method def eat (self): print ("students are eating") student1=Student ('Zhang San', 19) student2=Student ('Li Si' 20) print (id (student1)) # 2363920157896print (id (student2)) # 2363920157960print ("- bind attribute -") print ("bind attribute-dynamic binding gender property for student2 -") student2.gender=' male 'print (student1.name,student1.age) # Zhang San 19#print (student1.gender) when student1 accesses attributes that it does not have Error AttributeError: 'Student' object has no attribute' gender'print (student2.name,student2.age,student2.gender) # Li Si 20 male print ("- bind method -") def show (): print ('I am the show method') student1.show=showstudent1.show () # I am the show method student2.show () # error AttributeError: 'Student' object has no attribute' show'

Memory analysis:

VII. Three major features of object-oriented

1. Encapsulation

Class Car: def _ _ init__ (self,brand,age): self.brand=brand self.__age=age def show (self): print (self.brand,self.__age) car1=Car ('BMW X5 minute print 50) print (car1.brand) # the attribute of the BMW Xbike print (car1.__age) _ _ logo restricts its use outside the class, and can be used inside the class. External access will report an error # to use the attribute identified by _ _, you can first use dir () to find the attribute Then access print (dir (car1)) # output ['_ Car__age','_ _ class__','_ _ delattr__','_ _ dict__','_ _ dir__','_ _ doc__','_ _ eq__','_ format__','_ ge__','_ getattribute__','_ gt__','_ _ hash__','_ init__' '_ _ init_subclass__',' _ _ le__','_ _ lt__','_ _ module__','_ _ ne__','_ _ new__','_ _ reduce__','_ _ reduce_ex__','_ _ repr__','_ _ setattr__','_ sizeof__','_ str__','_ subclasshook__','_ _ weakref__' 'brand',' show'] print (car1._Car__age) # 50

2. Inheritance (unlike other languages, python supports multiple inheritance)

For example:

Class People: def _ init__ (self,name,age): self.name=name self.age=age def info (self): print (self.name,self.age) class Student (People): def _ init__ (self,name,age,sno): super (). _ init__ (name,age) self.sno=snoclass Teacher (People): def _ init__ (self,name,age) Teachofage): super (). _ init__ (name,age) self.teachofage=teachofagestudent1=Student ('Zhang San', 18122) teacher1=Teacher ('Li Si', 36 Magi 10) student1.info () # Zhang San 18teacher1.info () # Li Si 368, method rewrite

For example:

Class People: def _ init__ (self,name,age): self.name=name self.age=age def info (self): print (self.name,self.age) class Student (People): def _ init__ (self,name,age,sno): super (). _ init__ (name) Age) self.sno=sno def info (self): super (). Info () print (self.sno) class Teacher (People): def _ init__ (self,name,age,teachofage): super (). _ init__ (name,age) self.teachofage=teachofage def info (self): super (). Info () print (self.teachofage) student1=Student ('Zhang San', 18122) teacher1=Teacher ('Li Si') 36 student1.info 10) teacher1.info ()

The result is:

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