基于实例变量值实现类方法（面向对象编程）

huangapple
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英文:

Implement class method based on instance variable values (OOP)

问题

I am new to OOP. I want to create objects that have a method which depends on the instance variables value.

  1. class cases:
  2.     def __init__(self, a):
  3.         self.a = a  
  5.     def f1(self, x):
  6.         return x
  8.     def f2(self, x):
  9.         return 100*x
  10.         
  11.     if self.a < 3:
  12.         self.x = f1
  13.     else:
  14.         self.x = f2

If I create the following instances c1 and c2 by the class cases:

  1. c1 = cases(2)
  2. c2 = cases(5)

and execute the method x() I expect that:

  1. c1.x(10)  # --> 10
  2. c2.x(10)  # --> 1000

But right now the error is:

  1. NameError: name 'self' is not defined

If I change self.a to just a in the class definition, the error is:

  1. NameError: name 'a' is not defined

So how can I access the variable instance for a case discrimination?

UPDATE
By following the instructions of @deceze (2nd try). Code becomes as follows:

  1. def f1(x):
  2.     return x
  4. def f2(x):
  5.     return 100*x
  7. class case:
  8.     def __init(self, a):
  9.         self.a = a
  10.        
  11.     def x(self, x):
  12.         if self.a < 3:
  13.             return f1(x)
  14.         else:
  15.             return f2(x)
  16.           
  17. # make instances with different cases    
  18. c1 = case(2)
  19. c2 = case(4)
  21. # show results
  22. print(c1.x(10))
  23. print(c2.x(10))

Result is as desired.

英文:

I am new to OOP. I want to create objects that have a method which depends on the instance variables value.

  1. class cases:
  2.     def __init__(self, a):
  3.         self.a = a  
  4.   
  5.     def f1(self, x):
  6.         return x
  8.     def f2(self, x):
  9.         return 100*x
  10.         
  11.     if self.a < 3:
  12.         self.x = f1
  13.     else:
  14.         self.x = f2

If I create the following instances c1 and c2 by the class cases:

  1. c1 = cases(2)
  2. c2 = cases(5)

and execute the method x() I expect that:

  1. c1.x(10)  # --> 10
  2. c2.x(10)  # --> 1000

But right now the error is:

  1. NameError: name 'self' is not defined

If I change self.a to just a in the class definition, the error is:

  1. NameError: name 'a' is not defined

So how can I access the variable instance for a case discrimination?

UPDATE
By following the instructions of @deceze (2nd try). Code becomes the followed:

  1. def f1(x):
  2.     return x
  4. def f2(x):
  5.     return 100*x
  7. class case:
  8.     def __init__(self, a):
  9.         self.a = a
  10.        
  11.     def x(self, x):
  12.         if self.a < 3:
  13.             return f1(x)
  14.         else:
  15.             return f2(x)
  16.           
  17. # make instances with different cases    
  18. c1 = case(2)
  19. c2 = case(4)
  21. # show results
  22. print(c1.x(10))
  23. print(c2.x(10))

Result is as desired.

答案1

得分: 2

You are mixing up instances and parameters.

  1. def f1(x):
  2.     return x
  4. def f2(x):
  5.     return 100 * x
  7. class case:
  8.     def __init__(self, a):
  9.         self.a = a
  11.     def x(self, a):
  12.         if self.a < 3:
  13.             return f1(a)
  14.         else:
  15.             return f2(a)
  17. # make instances with different cases
  18. c1 = case(2)
  19. c2 = case(4)
  21. # show results
  22. print(c1.x(10))
  23. print(c2.x(10))

Output as expected.

英文:

You are mixing up instances and parameters.

  1. def f1(x):
  2.     return x
  4. def f2(x):
  5.     return 100*x
  9. class case:
  10.     def __init__(self, a):
  11.         self.a = a
  12.    
  13.     def x(self, a):
  14.         if self.a &lt; 3:
  15.             return f1(a)
  16.         else:
  17.             return f2(a)
  18.       
  19. # make instances with different cases    
  20. c1 = case(2)
  21. c2 = case(4)
  23. # show results
  24. print(c1.x(10))
  25. print(c2.x(10))

Output as expected.

huangapple
  • 本文由 发表于 2023年4月4日 17:10:05
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  • class
  • oop
  • python
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