I think it should be simple, but could not find correct way ore related document then hope to know way. 

Now I have active armature as "amt" , and it have many ID properties for shape keys and drive some bones. eg amt["prop1"] = 1.0, amt["prop2"] = 0.2 etc,,

by bpy, I can get amt ID property keys and values of current frame, which I only need to export, as python dictionary. 

eg preset = {"prop1":1.0, "prop3" :0.2,,,}

Now I hope to export the dictionary as json, 
then import the saved json , and apply these ID property values for current active armature, when I need. (of course it have same ID property keys)
 (I prefer to export as json,,)