Due to limited time, we evaluated SNM [Yin and Neubig, 2017] on Python dataset.5 SNM explicitly introduces the constraints of grammar rules when generating ASTs. The BLEU score for SNM is6 10.62 and similar to our Basic model, indicating that the CG task on this dataset is very challenging. In particular,7 all prediction of SNM is valid, whereas the percentage of valid code generated by the dual model is low (Table 1).8 Since CS and CG models are trained at the same time and the parameters of the36 two models are separate after the joint training, i.e., the two models solve their respective tasks separately after the37 joint training, the number of parameters of each dual model is the same as that of the basic model.