Python notes

Object oriented Foundation

I object-oriented

Object oriented Encyclopedia

II Classes and objects

1. Classes and objects

Encyclopedia of classes and objects

• class

Encyclopedia like

Class is a general term for a series of things with the same characteristics and behavior. It is an abstract concept. Class is used to create objects.
Characteristics are attributes and behaviors are methods

• object
  Objects are real things created by classes.

2. Pair oriented implementation method

• Define class
  The classes in Python 2 are divided into classic classes and new classes

  • grammar

  class Class name():
  	code
  	......
  

  Note: the class name must meet the identifier naming rules and follow the naming habit of large hump.

  • Examples

  class Dog():
  	def eat(self):
  		print('bone')
  

  • Classic class
    Classic class: a class that does not derive from any built-in type

    class Class name:
    	code
    	......
    

• create object
  Objects are also called instances.

  • grammar

  Object name=Class name()
  

  • Examples

  class Dog():
  	def eat(self):
  		print('bone')
  # create object
  d1=Dog()
  # d1 object calls instance method
  d1.eat() # bone
  

• self
  self refers to the object that calls the function.
  Examples

  class Dog():
      def eat(self):
          print('bone')
          print(self)
   # create object
   d1 = Dog() 
   print(d1) 
   # <__main__.Dog object at 0x0000010F1B4E9400>
  
   # d1 object calls instance method
   d1.eat()  
   # bone
   # <__main__.Dog object at 0x0000010F1B4E9400>
  
   d2 = Dog()
   print(d2) 
   # <__main__.Dog object at 0x0000010F1B4E94A8>
  
   # d2 object calls instance method
   d2.eat()  
   # bone
   # <__main__.Dog object at 0x0000010F1B4E94A8>
  

III Object properties

Attributes are characteristics.
Object properties can be added and obtained either outside the class or inside the class.

1. Add object attributes outside the class

• grammar

Object name.Attribute name=value

• Examples

d1.color='white'
d1.age=2

2. Get object properties outside the class

• grammar

Object name.Attribute name

• Examples

print(d1.color)
print(d1.age)

3. Get object properties in class

• grammar

self.Attribute name

• Examples

class Dog():
    def dog_info(self):
    	print(self.color)
    	print(self.age)
# create object
d1=Dog()

# Add instance properties
d1.color='white'
d1.age=2

d1.dog_info()
# whilte
# 2

IV Magic method

In Python__ xx__ () functions are called magic methods, which refer to functions with special functions.

1. init()
Function: initialize objects.

• Parameterless__ init__ ()

class Dog():
    # Define initialization function
    def __init__(self):
        # Add instance properties
        self.color='white'
        self.age=2
    def dog_info(self):
        # Call instance property in class
    	print(self.color)
    	print(self.age)
# create object
d1=Dog()
# Call method
d1.dog_info()
# white
# 2

Note:__ init__ () method, which is called by default when creating an object and does not need to be called manually__ init__ The self parameter in (self) does not need to be passed by the developer, and the python interpreter will automatically pass the current object reference.

• Parametric__ init__ ()

  • grammar

  def __init__(self,Attribute 1, attribute 2,...)
  	self.Attribute 1=Attribute 1
  	self.Attribute 2=Attribute 2
  	......
  

  • Examples

  class Dog():
      # Define initialization function
      def __init__(self,color,age):
          # Add instance properties
          self.color=color
          self.age=age
      def dog_info(self):
          # Call instance property in class
          print(self.color)
          print(self.age)
  # create object
  d1=Dog('white',2)
  d2=Dog('black',3)
  
  # Call method
  d1.dog_info()
  # white
  # 2
  
  d2.dog_info()
  # black
  # 3
  

2. str()
When print (object name) is used, the memory address of the object is printed by default. If the class is defined__ str__ () method, the return data in this method will be printed.

class Dog():
    # Define initialization function
    def __init__(self,color,age):
        # Add instance properties
        self.color=color
        self.age=age
    def __str__(self):
        return f'color: {self.color},age: {self.age}'

# create object
d1=Dog('white',2)

print(d1) # color: white,age: 2

3. del()
When an object is deleted, the python interpreter calls by default__ del__ () method.

class Dog():
    # Define initialization function
    def __init__(self,color,age):
        # Add instance properties
        self.color=color
        self.age=age
    def __del__(self):
        print(f'{self}Object deleted')
        
# create object
d1=Dog('white',2)

del d1 # <__ main__. Dog object at 0x000001ad5603b240 > object deleted

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