Example Python script to use from NiFi ExecuteScript processor which reads the first line from an incoming flow file.

read-flowfile-contents.py

from org.python.core.util.FileUtil import wrap

from org.apache.nifi.processors.script import ExecuteScript


first_line = None
flow_file = session.get()


def read_first_line(input):
    global first_line
    with wrap(input) as f:
        first_line = f.readline()


if flow_file:
    session.read(flow_file, read_first_line)
    if first_line:
        flow_file = session.putAttribute(flow_file, 'from-content', first_line)
        session.transfer(flow_file, ExecuteScript.REL_SUCCESS)