corrected exception error message

pyqtgraph/graphicsItems/PlotCurveItem.py

@@ -312,10 +312,10 @@ class PlotCurveItem(GraphicsObject):
         
         if self.opts['stepMode'] is True:
             if len(self.xData) != len(self.yData)+1:  ## allow difference of 1 for step mode plots
-                raise Exception("len(X) must be len(Y)+1 since stepMode=True (got %s and %s)" % (str(x.shape), str(y.shape)))
+                raise Exception("len(X) must be len(Y)+1 since stepMode=True (got %s and %s)" % (self.xData.shape, self.yData.shape))
         else:
             if self.xData.shape != self.yData.shape:  ## allow difference of 1 for step mode plots
-                raise Exception("X and Y arrays must be the same shape--got %s and %s." % (str(x.shape), str(y.shape)))
+                raise Exception("X and Y arrays must be the same shape--got %s and %s." % (self.xData.shape, self.yData.shape))
         
         self.path = None
         self.fillPath = None