As per offline discussion, multiple developers declaring the constant for the same string and error messages. To avoid that only one developer should work on this task.
Suggestions:
We should have a common class for Constants (which are not module specific).
Made a constant.py file which contains the common Constants.
For module specific constants we should not declare them as Global variables if possible declare them as the Class variable.
For common error messages(if any) we can define functions in PGChildNodeView.
Already implemented.
Please incorporate the changes send by Yogesh.
I will send another patch for Yogesh's changes as needed more changes.