made it a bit more generic; naming

mainwin.py

@@ -47,13 +47,13 @@ class MainWindow(QMainWindow):
         self.sig_make_new_plot.emit(name, pd)
 
 
-    def append_data(self, name, xy):
+    def append_data(self, name, point):
         lst = self.lst
-        lst.append(name, xy)
+        lst.append(name, point)
         for sub in self.mdi.subWindowList():
             if sub.windowTitle() == name:
                 pd = lst.data[name]
-                sub.plot.setData(pd.xs, pd.ys)
+                sub.plot.setData(*pd.data)
 
 
     def on_select_list_item(self, index):

plotdesc.py

@@ -12,6 +12,11 @@ class PlotDescription:
         self.style = pg_plot_style()
 
 
+    @property
+    def data(self):
+        return (self.xs, self.ys)
+
+
     def append(self, xy):
         x, y = xy
         self.xs.append(x)