Learning: Python learning path (6): Class

Learning: Python learning path (6): class and Object

In layman's terms, classes are definitions, and objects are entities.

Simply put, people are classes, and Gao Peng is an object.

Attribute

Attributes include instance attributes and class attributes.

Let's take a look at the previous Code:

1. Class Fruit:
2. Price = 0
3.  
4. Def _ init _ (self ):
5. Self. color = 'red'
6. Zone = "china"
7.  
8. If _ name __= = "_ main __":
9. Print "Fruit price: % d" % Fruit. price
10. Apple = Fruit ()
11. Print "apple color: % s" % apple. color
12. Print "apple price: % d" % apple. price
13. Banane = Fruit ()
14. Print "banane color: % s" % banane. color
15. Print "banane price: % d" % banane. price
16.  
17. Fruit. color = "yellow"
18. Fruit. price = 50
19.  
20. Print "apple color: % s" % apple. color
21. Print "apple price: % d" % apple. price
22. Print "banane color: % s" % banane. color
23. Print "banane price: % d" % banane. price
24. # Result
25. Fruit price: 0
26. Apple color: red
27. Apple price: 0
28. Banane color: red
29. Banane price: 0
30. Apple color: red
31. Apple price: 50
32. Banane color: red
33. Banane price: 50

You can directly modify the class attributes of all classes through the class, but cannot modify the instance attributes.

Modify rows 17 and 18.

1. Class Fruit:
2. Price = 0
3.  
4. Def _ init _ (self ):
5. Self. color = 'red'
6. Zone = "china"
7.  
8. If _ name __= = "_ main __":
9. Print "Fruit price: % d" % Fruit. price
10. Apple = Fruit ()
11. Print "apple color: % s" % apple. color
12. Print "apple price: % d" % apple. price
13. Banane = Fruit ()
14. Print "banane color: % s" % banane. color
15. Print "banane price: % d" % banane. price
16.  
17. Apple. color = "yellow"
18. Apple. price = 50
19.  
20. Print "apple color: % s" % apple. color
21. Print "apple price: % d" % apple. price
22. Print "banane color: % s" % banane. color
23. Print "banane price: % d" % banane. price
24. # Result
25. Fruit price: 0
26. Apple color: red
27. Apple price: 0
28. Banane color: red
29. Banane price: 0
30. Apple color: yellow
31. Apple price: 50
32. Banane color: red
33. Banane price: 0

Modifying instance variables only affects the instance variables and the class attributes of the instance.

Let's try again.

1. Class Fruit:
2. Price = 0
3.  
4. Def _ init _ (self ):
5. Self. color = 'red'
6. Zone = "china"
7.  
8. If _ name __= = "_ main __":
9. Print "Fruit price: % d" % Fruit. price
10. Apple = Fruit ()
11. Print "apple price: % d" % apple. price
12. Banane = Fruit ()
13. Print "banane price: % d" % banane. price
14.  
15. Apple. price = 30
16. Fruit. price = 50
17.  
18. Print "apple price: % d" % apple. price
19. Print "banane price: % d" % banane. price
20. # Result
21. Fruit price: 0
22. Apple price: 0
23. Banane price: 0
24. Apple price: 30
25. Banane price: 50

If the class attribute of the instance is modified, it will be detached from the class attribute.

Class Method

1. Class Fruit:
2. Price = 0
3.  
4. Def _ init _ (self ):
5. Self. color = 'red'
6. Zone = "china"
7. Def printColor (self ):
8. Print "color:" + self. color
9. Def printPrice (self ):
10. Print "price: % d" % self. price
11. @ Staticmethod
12. Def printStatic ():
13. Print "static"
14.  
15.  
16.  
17. If _ name __= = "_ main __":
18. Fruit. printStatic ()
19. Apple = Fruit ()
20. Apple. printStatic ()
21. Apple. printPrice ()
22. Apple. printColor ()

The common method comes with the self parameter, which allows you to access instance attributes and class attributes through self. Static methods do not contain self parameters, nor can they access instance parameters and class parameters through self.

1. Class Fruit:
2. Price = 0
3. @ Staticmethod
4. Def printStatic ():
5. Print Fruit. price
6.  
7. If _ name __= = "_ main __":
8. Fruit. printStatic ()

It can only be accessed directly through a class.

Constructor and destructor

1. Class Fruit:
2. Count = 0
3. Def _ init _ (self ):
4. Print "I have been called"
5.  
6. Def _ del _ (self ):
7. Print "I was unfortunately called"
8.  
9. If _ name __= = "_ main __":
10. Apple = Fruit ()
11. # Result
12. I have been called
13. Unfortunately, I was called.
14.  
15.  
16. Class Fruit:
17. Count = 0
18. Def _ init _ (self ):
19. Print "I have been called"
20.  
21. Def _ del _ (self ):
22. Print "I was unfortunately called"
23.  
24. If _ name __= = "_ main __":
25. Apple = Fruit ()
26. Fruit. count
27. # Result
28. I have been called
29. Unfortunately, I was called.

Class initialization and destruction are called.

The class is not automatically called when it is called.

Summary

This time I made some basic introductions to the class. Next time we will talk about inheritance and polymorphism.