Question

I want to be able to return multiple objects of a class by using a method within the class. Something like this.

class A:
    def __init__(self,a):
    self.a = a

    def _multiple(self,*l):
        obj = []
        for i in l:
            o = self.__init__(self,i)
            obj.append(o)
        return obj

When I execute this on iPython (iPython 0.10 and Python 2.6.6) I get the following

In [466]: l = [1,2]
In [502]: A._multiple(*l)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

TypeError: unbound method _multiple() must be called with A instance as 
first argument (got int instance instead)

I’m definitely unclear about the invocation as well as the ‘self’ keyword usage. Could you help me out in getting this correct?

Thank you.

Answer 1

TypeError: unbound method _multiple() must be called with A instance
as first argument (got int instance instead)

The Error is self explanatory. It means that an instance method is being called as a Class method. To make the instance method as a class method add the decorator @classmethod

>>> class A:
    def __init__(self,a):
        self.a = a
    @classmethod
    def _multiple(cls,*l):
        #Create multiple instances of object `A`
        return [A(i) for i in l]

>>> l = [1,2]
>>> A._multiple(*l)
[<__main__.A instance at 0x066FBB20>, <__main__.A instance at 0x03D94580>]
>>>