update nested dictionary from another nested dictionary based on mapping provided in dictionary : I need to write down a method to transform existing nested dictionary values from another nested dictionary , and mapping in between these two dictionary is in another third dictionary. 

    source = { "s0" : 
                         {
                           "s1_f1":"s1_v1",
                           "s1_f2" : "s1_v2"
                         },
                         {
                           "s2_f1":"s2_v1",
                           "s2_f2" : "s2_v2",
                           "s2_f3" : {
                                        "s3_f1":"s3_v1"
                                     }
                         }
    
            }
    
    destinatin = { "d0" : 
                         {
                           "d1_f1":"d1_v1",
                           "d3_f1" :"d3_v1"
                         }
                }

    mapping = {
                "s1_f1":"d1_f1",
                "s3_f1" : "d3_f1"
              }

    result = {
    
      "d0" : 
                         {
                           "d1_f1":"s1_v1",
                           "d3_f1" :"s3_v1"
                         }
    
    }

I already checked couple of libraries for transformation but i want to write down the custom code for this. 

            
