NiFi: ExecuteStreamCommand STDIN and STDOUT

[#1]

Hi,

Can some one please give an example of STDIN and STDOUT in python script to take input from Nifi flowfile and paas the output file to NiFi flowfile again. I am using below script for STDIN and STDOUT. STDIN seems to be working fine but STDOUT is not working. Please help

f = sys.stdin
reader = csv.reader(f)

***********

##Python code for creating the output file and passing it to STDOUT

xmlfile = open("C:\\Output_from_python\\output_file.xml",'w')
xmlFile.write(doc.toprettyxml(indent = '\t'))
xmlFile.close()
sys.stdout = xmlFile

[#2]

Just simple print it.