Please, how do I call the method inside this class

[Yoriz]

You have

print(''.join(str(next(self) for j in range(n))))

which is turning a generator into a string str(next(self) for j in range(n))
i think what you are looking for is

print(''.join(str(next(self)) for j in range(n)))

which is turning the next item into a string str(next(self))

---

The following

print(type(i for i in range(2)))

creates a generator

Output:
<class 'generator'>

whereas including square brackets

print(type([i for i in range(2)]))

creates a list

Output:
<class 'list'>