调整缩放出现Error in getting scale

import arcpy
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]
layer = arcpy.mapping.ListLayers(mxd, "layer1", df)[0]
arcpy.SelectLayerByAttribute_management(layer , "NEW_SELECTION")
df.extent = accidentLayer.getSelectedExtent(False)
df.scale = df.scale * 1.5
arcpy.RefreshActiveView()
运行后出现错误ValueError: DataFrameObject: Error in getting scale,请问该如何解决？