loop.py

"""
Snippet to show how to make a loop run at a given frequency without drift.
"""

import signal
import time
from abc import ABCMeta, abstractmethod

DT_DISPLAY = 0.04  # 25 fps


class Loop(metaclass=ABCMeta):
    """
    Astract Class to allow users to execute self.loop at a given frequency 
    with a timer while self.run can do something else.
    """
    def __init__(self, period):
        self.period = period
        signal.signal(signal.SIGALRM, self.loop)
        signal.setitimer(signal.ITIMER_REAL, period, period)
        self.run()

    def stop(self):
        signal.setitimer(signal.ITIMER_REAL, 0)

    @abstractmethod
    def run(self):
        ...

    @abstractmethod
    def loop(self, signum, frame):
        ...


class Viewer(Loop):
    def __init__(self, *args, **kwargs):
        self.t = 0
        super().__init__(*args, **kwargs)

    def loop(self, signum, frame):
        self.t += self.period
        print(f'robot.display(q_t({self.t}))')
        if self.t >= 5:
            self.stop()

    def run(self):
        # we don't actually need anything here, just sleep.
        try:
            time.sleep(1e9)
        except KeyboardInterrupt:
            pass

    def stop(self):
        super().stop()
        raise KeyboardInterrupt  # our self.run is waiting for this.


if __name__ == '__main__':
    Viewer(DT_DISPLAY)

$ /usr/bin/time python loop.py
[…]
0.05user 0.01system 0:05.06elapsed 1%CPU (0avgtext+0avgdata 9560maxresident)