如何安排函数在第一次在 python 中运行后每 3 天运行一次

Question

我有一个函数，我需要在 3 天后使用 python 运行它

def hello()
print("hello world")

脚本将运行，如何在python中每3天打印一次

Answer 1

正如@Nuts 在评论中所说，如果您想每三天运行一次整个程序，cron 是最佳选择。但是，如果您正在运行微服务或其他东西，并且只想每三天执行一次特定方法，则可以使用计时器。

import threading

my_timer = None

def make_thread():
    # create timer to rerun this method in 3 days (in seconds)
    global my_timer
    my_timer = threading.Timer(259200, make_thread)
    # call hello function
    hello()

只需调用一次make_thread() 以第一次执行hello()，然后它会每三天调用一次（很可能会有几秒钟的错误余量），只要程序保持运行。

Answer 2

如果你必须使用 python，一种可能的方法（稍微改编自 this 线程，它有其他好的信息）是使用大量的睡眠语句。

#!/usr/bin/python3

import time 

def hello():
    print("Hello, World")

while True:
    hello()
    time.sleep(3*24*60*60) 

这里有一个更完整的代码sn-p。我测试了较短的时间间隔（不是 3 天），但它应该可以工作

import numpy as np 
import time
import datetime

def function_to_call_periodically():
    print("Hello World")

# specify the interval and the time (3 days and at 11h00)
# The code below assumes the interval is more than a day
desired_time_delta_in_seconds = 3*24*60*60  # 3 days
desired_time_minutes = 00
desired_time_hours = 11

# set the starting time the code will run every 3 days from this date (at the specified time)
start_date = datetime.datetime(2018, 8, 7) # year, month date (hours, minutes, seconds will all be zero)
start_stamp = start_date.timestamp()

# if the scripts gets restarted we need to figure out when the next scheduled function call is 
# so we need to nkow when we started
curr_time = datetime.datetime.now()
curr_stamp = curr_time.timestamp()
last_interval = (curr_stamp - start_stamp) // desired_time_delta_in_seconds


# Loop forever
while(True):
    # sleep so we don't use up all the servers processing power just checking the time
    time.sleep(5)

    # get the current time and see how many whole intervals have elapsed
    curr_time = datetime.datetime.now()
    curr_stamp = curr_time.timestamp()
    num_intervals = (curr_stamp - start_stamp) // desired_time_delta_in_seconds # python 3 integer division

    # if at least another interval has elapsed and it is currently the time for the next call
    # then call the function and update the interval count so we don't call it again
    if (num_intervals > last_interval) and (curr_time.hour >= desired_time_hours) and (curr_time.minute >= desired_time_minutes):
        print("Calling scheduled function at ", curr_time)
        last_interval = num_intervals
        function_to_call_periodically()