def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def __init__(self, w, h, color = "empty"):
		self.board = zeros((h,w), dtype=uint8)
		self.w = w
		self.h = h
		self.set_brush(color)