generic Class in Python

Question

I want to do a generic class in Python with one method

This class does not generate its instances
Some attributes are set in the body of the class
Method of this class uses the set attributes and in the generated classes the output of this method depends on these attributes
Method has only one input

I know that without metaclasses will not do, but I do not know how to apply them :)

something like this:

class GenericClass:
  attr_a = ''
  attr_b = ''
  def count(text):
    return len(text)/attr_a + attr_b

class A(GenericClass):
  attr_a = 2
  attr_b = 1

text = "Hello, I'm under the water"
print(A.count(text))
# 14

What do you mean by "This class does not generate its instances"? That it should be impossible to create instances of it? — Jack Taylor
– Jack Taylor, Commented Dec 21, 2022 at 9:45
It definitely sounds like you want @classmethod. You will still be able to instantiate classes that use this, but @classmethod will do most of what you want. If you also want to stop people from instantiating the class, you could also raise an error inside the __init__ method. — Jack Taylor
– Jack Taylor, Commented Dec 22, 2022 at 1:28

deceze · Accepted Answer · 2022-12-21 09:51:18Z

1

Defining count as a class method would make that work:

@classmethod
def count(cls, text):
    return len(text) / cls.attr_a + cls.attr_b

answered Dec 21, 2022 at 9:51

deceze♦

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cionzo · Accepted Answer · 2022-12-21 09:52:32Z

0

class GenericClass:
    def _count(text, a, b):
        return len(text)/a + b

class A(GenericClass):
    attr_a = 2
    attr_b = 1

    def count(text):
        return GenericClass._count(text, A.attr_a, A.attr_b)
    
text = "Hello, I'm under the water"
print(A.count(text))

answered Dec 21, 2022 at 9:52

cionzo

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1 Comment

deceze Over a year ago

That requires you to reimplement count on every subclass… Not very generic.

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