Thanks a lot @Matt Burgess , By adding reference self to the variable as 'self.total', It did miracle. code snippet is working absolutely fine as expected. It really helps me a lot. import traceback from org.apache.nifi.processors.script import ExecuteScript from org.apache.nifi.processor.io import StreamCallback from java.io import BufferedReader, InputStreamReader, OutputStreamWriter class ConvertFiles(StreamCallback) : def __init__(self) : pass def process(self, inputStream, outputStream) : try : self.total = 0 reader = InputStreamReader(inputStream,"UTF-8") bufferedReader = BufferedReader(reader) writer = OutputStreamWriter(outputStream,"UTF-8") line = bufferedReader.readLine() while line != None: ChangedRec = line.upper() writer.write(ChangedRec) writer.write('\n') a=line.split(",") for valu in a: b=valu.strip() self.total += int(b) line = bufferedReader.readLine() print("Summation of Records are %s ",self.total) writer.flush() writer.close() reader.close() bufferedReader.close() except : print "Exception in Reader:" print '-' * 60 traceback.print_exc(file=sys.stdout) print '-' * 60 raise session.transfer(flowFile, ExecuteScript.REL_FAILURE) finally : if bufferedReader is not None : bufferedReader.close() if reader is not None : reader.close() flowFile = session.get() if flowFile is not None : ConvertFilesData = ConvertFiles() session.write(flowFile, ConvertFilesData) flowFile = session.putAttribute(flowFile, "FileSum",str(ConvertFilesData.total)) session.transfer(flowFile, ExecuteScript.REL_SUCCESS) Snapshot Result: ... View more