My data is coming in text (ASCII) files, with each line having a fixed number of fields and each field having a fixed length. I want to convert this files to CSV, like this: Input line: abbccc Output line: a,bb,ccc I the example above "a", "bb", "ccc" are fields of fixed length. So, I always know exactly how to split the input line.   I looked into the ConvertRecord operator and the ScriptedReader controller service (that can be used as a record reader), but I was not able to find any example of a Python script for ScriptedReader. I found this ExecuteScript Cookbook by @mburgess, but those recipes are much more general, so I cannot use them in SciptedReader (which needs very specific objects for record processing that must be created by the script).   Can anyone give a basic example of a Python script that can be used in ScriptedReader to process records?   Alternatively, is there another way to accomplish the task (another processor)? Of course, I can use ExecuteScript processor and script the processing of complete FlowFiles in it, but my FlowFiles contain millions of records and I think this processing will be much more inefficient than SciptedReader. ... View more