Python Note: Object-Oriented

The basic theory

What is the object

Everything Is an Object

Objects are specific things

• Have attributes, behaviors
• The many scattered things, the package as a whole

Everything in Python is an object, Python is a particularly thorough language of object-oriented programming (OOP)

Many other programming languages ​​also points primitive types and object types, while in python, only the object type

& Object-oriented process-oriented

Both are problem-solving ideas, thoughts, object-oriented itself is a process-oriented package

• Process-oriented: In solving problems, attention is to solve the problem of every process (step)
  • Follow the steps in division
  • Put a task is decomposed into each of the specific steps
• Object-oriented: In solving problems, attention is needed to solve the problem objects
  • Divided according to functional objects
  • Find the object, to determine the properties and behavior of objects
• How object from process-oriented to face:
  • Task Steps list
  • And object separation step function block
  • The function code is divided into specific object
  • The specific behavior of objects and, based extract

class

What is the class

Abstract class is a particular class of object features

The role of class

The abstract class, the production of specific objects

The composition of the class

Name, properties, methods

note:

• Properties and methods, are abstract concepts
• After generating the object, the object has only a specific attribute values, and means to achieve

The relationship between objects and classes

Objects - Abstract - class

Class - Examples of - objects

The definition of class

Classic definition:

class 类名:
    ......

Create an object

obj = 类名()

The underlying operation when creating an object:

• Will first open up some space in memory (define classes will take up memory)
• Get the class name through the class variables:xxx.__name__
• Get the class through an object:xxx.__class__

Property related

The difference between attributes and variables

concept:

• Variables: value can be changed
• Property is: are the characteristics of an object

access permission:

• Variables: Depending on the scope, there are different access rights
• Properties: you can only be accessed through the object
  • The object is referenced by variables, scopes also have rights

Judgments based:

• Whether there is a host

Add property

1. Directly through the object, add the dynamic
   • grammar:对象.属性 = 值
2. Initialization method (constructor) by class
   • __init__()

With the addition of a property, to open up some space in memory to store the property value, then this value is stored in the object space where the object reference variables

Access Properties

Directly 对象.属性access

python provides a __dict__property is a dictionary, which now contains all the properties of this object

Modify the properties

Modify property value:对象.属性 = 值

Delete property

del 对象.属性

Class Properties

Increase class attributes:

• 类名.属性 = 值
• In class, write directly 属性 = 值

View class properties:

• 类名.属性
• Class attributes can also be accessed via the object:对象.类属性
• Object Properties discovery mechanisms:
  • Priority to the object itself to find properties, find the end
  • If not found, according to __class__find an object corresponding to the class, look for this class of property

Modify class properties:

• Modified by the class name:类名.属性 = 值
• 对象.__class__.属性 = 值
• Note: You can not be modified directly through the object! 对象.属性 = xxxIncreasing property and modify the properties of the grammatical object

View all class attributes:类名.__dict__

Remove class attributes:

• del 类名.属性
• Objects can not be deleted, del can only delete the object of direct property

Memory storage problem class attributes:

• Properties are stored in a dictionary, this dictionary is real, can __dict__be accessed
• 类.__dict__It is a read-only property
• to sum up:
  • In general, the properties are stored in __dict__the dictionary, some built-in objects do not have this property
  • You can directly modify the general object __dict__attributes
  • But the class of the object __dict__is read-only, can not be modified by default, can be modified by means of setattr

Each object class attribute is shared:

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