Rate-limiting utility for tracing and such

periodically.py

#!/usr/bin/env python3
from time import monotonic

class periodically:
	def __init__(self, interval):
		self.interval = interval
		self._previous = None

	def __enter__(self):
		if self._previous is not None:
			raise RuntimeError
		self._previous = monotonic()
		return self

	def __bool__(self):
		if self._previous is None:
			raise RuntimeError
		now = monotonic(); elapsed = now - self._previous
		if elapsed >= self.interval:
			self._previous = now - elapsed % self.interval
			return True
		else:
			return False

	def __exit__(self, exc_type, exc_value, exc_tb):
		if self._previous is None:
			raise RuntimeError
		self._previous = None

if __name__ == '__main__':  # test and demonstration
	from time import sleep
	with periodically(2) as trace:
		start = monotonic()
		for i in range(20):
			sleep(.75)
			if trace: print(i, monotonic() - start)