'add other to my value and return self
>>> c = Counter(100)
>>> c += 333
>>> c == 433
True'

def __iadd__(self, other):

    if ((self.maxval is not None) and ((self._count + other) > self.maxval)):
        raise ValueError('sorry,    counter    got    too    big')
    else:
        self._count += other
    return self
