#!/usr/bin/env python3.4

import datetime
import time

def something():
    print(datetime.datetime.now())
    # Simulate long running task
    time.sleep(0.75)

start = datetime.datetime.now()
if True:
    start = start.replace(microsecond=0)

while True:
    something()

    target = start + datetime.timedelta(seconds=1)
    while target > datetime.datetime.now():
        sleep_time = (target - datetime.datetime.now()).total_seconds()
        time.sleep(sleep_time)
    start = target