Periodic write to file every second.

periodic_task.py

import sched, time
from datetime import datetime

s = sched.scheduler(time.time, time.sleep)

def read_signal(sc):
    with open('/home/vasek/Downloads/test.csv', 'a') as log:
        log.write('{timestamp},{temperature}\n'.format(timestamp=datetime.now(), temperature=23.0))
    # do your stuff
    s.enter(1, 1, read_signal, (sc,))

s.enter(1, 1, read_signal, (s,))
s.run()