我想在Python中每60秒重复执行一个函数(就像Objective C中的NSTimer或JS中的setTimeout)。这段代码将作为守护进程运行,有效地类似于使用cron每分钟调用python脚本,但不需要用户设置。

在这个关于用Python实现的cron的问题中,解决方案似乎只有效地使()休眠x秒。我不需要这么高级的功能,所以也许这样的东西可以工作

while True:
    # Code executed here
    time.sleep(60)

这段代码是否存在任何可预见的问题?


当前回答

它和cron之间的主要区别是异常会永久地杀死守护进程。您可能希望使用异常捕获器和记录器进行包装。

其他回答

我认为更简单的方法是:

import time

def executeSomething():
    #code here
    time.sleep(60)

while True:
    executeSomething()

这样,你的代码被执行,然后等待60秒,然后再次执行,等待,执行,等等…… 没有必要把事情复杂化:D

如果您的程序还没有事件循环,请使用sched模块,它实现了一个通用的事件调度器。

import sched, time

def do_something(scheduler): 
    # schedule the next call first
    scheduler.enter(60, 1, do_something, (scheduler,))
    print("Doing stuff...")
    # then do your stuff

my_scheduler = sched.scheduler(time.time, time.sleep)
my_scheduler.enter(60, 1, do_something, (my_scheduler,))
my_scheduler.run()

如果您已经在使用事件循环库,如asyncio、trio、tkinter、PyQt5、gobject、kivy等,则只需使用现有事件循环库的方法来调度任务。

import time, traceback

def every(delay, task):
  next_time = time.time() + delay
  while True:
    time.sleep(max(0, next_time - time.time()))
    try:
      task()
    except Exception:
      traceback.print_exc()
      # in production code you might want to have this instead of course:
      # logger.exception("Problem while executing repetitive task.")
    # skip tasks if we are behind schedule:
    next_time += (time.time() - next_time) // delay * delay + delay

def foo():
  print("foo", time.time())

every(5, foo)

如果你想在不阻塞剩余代码的情况下这样做,你可以使用这个让它在自己的线程中运行:

import threading
threading.Thread(target=lambda: every(5, foo)).start()

该解决方案结合了其他解决方案中很少结合的几个特性:

Exception handling: As far as possible on this level, exceptions are handled properly, i. e. get logged for debugging purposes without aborting our program. No chaining: The common chain-like implementation (for scheduling the next event) you find in many answers is brittle in the aspect that if anything goes wrong within the scheduling mechanism (threading.Timer or whatever), this will terminate the chain. No further executions will happen then, even if the reason of the problem is already fixed. A simple loop and waiting with a simple sleep() is much more robust in comparison. No drift: My solution keeps an exact track of the times it is supposed to run at. There is no drift depending on the execution time (as in many other solutions). Skipping: My solution will skip tasks if one execution took too much time (e. g. do X every five seconds, but X took 6 seconds). This is the standard cron behavior (and for a good reason). Many other solutions then simply execute the task several times in a row without any delay. For most cases (e. g. cleanup tasks) this is not wished. If it is wished, simply use next_time += delay instead.

例如:显示当前本地时间

import datetime
import glib
import logger

def get_local_time():
    current_time = datetime.datetime.now().strftime("%H:%M")
    logger.info("get_local_time(): %s",current_time)
    return str(current_time)

def display_local_time():
    logger.info("Current time is: %s", get_local_time())
    return True

# call every minute
glib.timeout_add(60*1000, display_local_time)

我最终使用了时间表模块。API很好。

import schedule
import time

def job():
    print("I'm working...")

schedule.every(10).minutes.do(job)
schedule.every().hour.do(job)
schedule.every().day.at("10:30").do(job)
schedule.every(5).to(10).minutes.do(job)
schedule.every().monday.do(job)
schedule.every().wednesday.at("13:15").do(job)
schedule.every().minute.at(":17").do(job)

while True:
    schedule.run_pending()
    time.sleep(1)