Python entry basis (9) __ object-oriented programming _2

• __str__ method

　　If in development, want to use the print output object variable, the ability to print customized content, you can use the built-in method of __str__

　　Note: __ str__ method must return a string

class Cat ():
     DEF  the __init__ (Self, name): 
        the self.name = name
         Print ( ' cat come% s ' % the self.name) 

    DEF  __str__ (Self):
         return  ' % s love fish ' % Self. name 

# create objects, pass in the parameter 
A = Cat ( ' Tom ' )
 Print (A)

result:

Tom the cat came 
Tom love fish

 

• Private property --- package

Sometimes a property or method of the object that we want to be used only inside the object and do not want to be accessed externally

　　Defined way

When you define a property or method to increase before the property name or method name two underscores __, in fact, during development, private property is not static, so give private property can provide external operating methods

　　By custom get, set methods provide access to private property

class the Person ():
     DEF  __init__ (Self, name, Age): 
        self.name = name 
        . Self __age = Age 

# definition of private property get method to acquire private property 
    DEF getAge (Self):
         return Self. __age 

# definition of private the method set reassignment property, private property reset 
    DEF the setAge (Self, Age): 
        . Self __age = Age 

PERSON1 = the Person ( ' Tom ' ,. 19 ) 
person1.setAge ( 20 is )
 Print (person1.name, person1.getAge ())

result

Tom 20

 

You can also use the property offers private label attribute access

• Class properties, class methods, static methods

Object class is created: the class object: instance of an object class name

Class is the class object properties owned property, which is shared by all the class of the object instance of the object, there is only one copy in memory. For the class of public property, can be accessed through the class object and instance objects outside the class

class people (): 
    name = ' Tom ' 
    __age =. 19 

P = people
 Print (p.name) # instance object 
Print (people.name) # class object 

# error, can not be accessed outside the class private class attributes 
# Print (P Age .__) 
# Print (people .__ Age)

result

tom 
tom

If the modified class properties outside the class, have to go through the class object is then modified, if a reference to an object by way of example, will produce an instance property of the same name, this modified embodiment is modified instance attribute, and the attribute will not affect the class If you reference the name of the property by way of example object instance attributes will force shield the class attribute that references an instance property, unless the property delete instance

　　Class Methods

Method variables have the class object, decorator @classmethod need to identify which type of process for a class method, the first parameter must be a class object, generally cls as the first parameter (other names may be used as the first argument), it is possible to access the object and the class object by way of example

#类方法
class people():
    country = 'country'

    @classmethod
    def getCountry(cls):
        return cls.country

p = people()
print(p.getCountry())
print(people.getCountry())

result

country
country

　　Static method

Need to be modified by modifying an @staticmethod, the static method does not require custom parameter

#静态方法
class people():
    China = 'China'

    @staticmethod
    def getCountry():
        return people.China

p = people()
print(p.getCountry())
print(people.getCountry())

result

China 
China