以下のようにすれば良さそうなんだが、妙に面倒臭い...。
cur_layer = Glyphs.font.selectedLayers[0] path = GSPath() pt = NSPoint(0, 0) node = GSNode(pt, type="line") path.nodes.append(node) pt = NSPoint(100, 0) node = GSNode(pt, type="line") path.nodes.append(node) pt = NSPoint(100, 100) node = GSNode(pt, type="line") path.nodes.append(node) path.closed = True cur_layer.paths.append(path)