Question

I’m implementing several constructors using @classobj. I’m not only setting variables, but also calling methods in the new class:

class Example:
    def __init__(self):
        pass

    @classmethod
    def constructor1(cls,x,y):
        self=cls
        self.__x = x
        self.__somemethod(self,y)

    ...

I get the following error:

unbound method __somemethod() must be called with Example instance as 
first argument (got classobj instance instead)

How do I resolve this problem?

Answer 1

If you’re wanting your class method to be a constructor, you probably want to be creating an instance of the class you get passed in as cls. I suspect you’re trying to do that with your self = cls line, but you’re not actually creating a new instance because you’ve neglected to put parentheses. There are some other issues too, but I think that is the key one. Here’s a fixed constructor:

@classmethod
def constructor1(cls,x,y):
    self=cls()                # parentheses added, to make it a call
    self.__x = x
    self.__somemethod(y)      # self is not needed as a parameter here
    return self               # return the new instance