Least painful way to run a Python delay loop

Question

I've got an event-driven chatbot and I'm trying to implement spam protection. I want to silence a user who is behaving badly for a period of time, without blocking the rest of the application.

Here's what doesn't work:

if user_behaving_badly():
  ban( user )
  time.sleep( penalty_duration )  # Bad! Blocks the entire application!
  unban( user )

Ideally, if user_behaving_badly() is true, I want to start a new thread which does nothing but ban the user, then sleep for a while, unban the user, and then the thread disappears.

According to this I can accomplish my goal using the following:

if user_behaving_badly():
  thread.start_new_thread( banSleepUnban, ( user, penalty ) )

"Simple" is usually an indicator of "good", and this is pretty simple, but everything I've heard about threads has said that they can bite you in unexpected ways. My question is: Is there a better way than this to run a simple delay loop without blocking the rest of the application?

Answer 1

instead of starting a thread for each ban, put the bans in a priority queue and have a single thread do the sleeping and unbanning

this code keeps two structures a heapq that allows it to quickly find the soonest ban to expire and a dict to make it possible to quickly check if a user is banned by name

import time
import threading
import heapq

class Bans():
    def __init__(self):
        self.lock = threading.Lock()
        self.event = threading.Event()
        self.heap = []
        self.dict = {}
        self.thread = threading.thread(target=self.expiration_thread)
        self.thread.setDaemon(True)
        self.thread.start()

    def ban_user(self, name, duration):
        with self.lock:
            now = time.time()
            expiration = (now+duration) 
            heapq.heappush(self.heap, (expiration, user))
            self.dict[user] = expiration
            self.event.set()

    def is_user_banned(self, user):
        with self.lock:
            now = time.time()
            return self.dict.get(user, None) > now

    def expiration_thread(self):
        while True:
            self.event.wait()
            with self.lock:
                next, user = self.heap[0]
                now = time.time()
                duration = next-now
            if duration > 0:
                time.sleep(duration)
            with self.lock:
                if self.heap[0][0] = next:
                    heapq.heappop(self.heap)
                    del self.dict(user)
                if not self.heap:
                    self.event.clear()

and is used like this:

B = Bans()
B.ban_user("phil", 30.0)
B.is_user_banned("phil")