List attributes of an object

Is there a way to grab a list of attributes that exist on instances of a class?

class new_class():
    def __init__(self, number):
        self.multi = int(number) * 2
        self.str = str(number)

a = new_class(2)
print(', '.join(a.SOMETHING))

The desired result is that "multi, str" will be output. I want this to see the current attributes from various parts of a script.