I would likely use the second approach, possibly using None to indicate invalid data. It is true that it is difficult to read/maintain if you add attributes later. However, more information on the purpose of this class/object would give insight as to why the first idea is a bad design: where would you ever have a completely empty class with no methods or default data? Why wouldn't you know what attributes the class has?

It's possible that processData might be better as a method (process_data to follow python naming conventions), since it acts upon the class. Given the example, it looks like it might be better as a data structure (where a dict may suffice).

Given a real example, you might consider taking the question to CodeReview, where they could help to refactor the code.

I would likely use the second approach, possibly using None to indicate invalid data. It is true that it is difficult to read/maintain if you add attributes later. However, more information on the purpose of this class/object would give insight as to why the first idea is a bad design: where would you ever have a completely empty class with no methods or default data? Why wouldn't you know what attributes the class has?

It's possible that processData might be better as a method (process_data to follow python naming conventions), since it acts upon the class. Given the example, it looks like it might be better as a data structure (where a dict may suffice).

Given a real example, you might consider taking the question to CodeReview, where they could help to refactor the code.