如何在给定时间后终止程序在Python中的运行

Question

I'd like my Python program to run an algorithm for a given number of seconds and then to print the best result so far and to end.

What is the best way to do so?

I tried the following but it did not work(the program kept running after the printing):

def printBestResult(self):
    print(self.bestResult)
    sys.exit()

def findBestResult(self,time):
    self.t = threading.Timer(time, self.printBestResult)
    self.t.start() 

    while(1):
        # find best result

Answer 1

Untested code, but something like this?

import time    
threshold = 60
start = time.time()

best_run = threshold
while time.time()-start < threshold:
   run_start = time.time()
   doSomething()
   run_time = time.time() - start
   if run_time < best_run:
       best_run = run_time

Answer 2

On unix, you can use signals -- This code times out after 1 second and counts how many times it iterates through the while loop in that time:

import signal
import sys

def handle_alarm(args):
    print args.best_val
    sys.exit()

class Foo(object):
    pass

self=Foo() #some mutable object to mess with in the loop
self.best_val=0
signal.signal(signal.SIGALRM,lambda *args: handle_alarm(self))

signal.alarm(1) #timeout after 1 second
while True:
    self.best_val+=1 # do something to mutate "self" here.

Or, you could easily have your alarm_handler raise an exception which you then catch outside the while loop, printing your best result.

Answer 3

If you want to do this with threads, a good way is to use an Event . Note that signal.alarm won't work in Windows, so I think threading is your best bet unless in that case.

import threading
import time
import random

class StochasticSearch(object):
    def __init__(self):
        self.halt_event = threading.Event()

    def find_best_result(self, duration):
        halt_thread = threading.Timer(duration, self.halt_event.set)
        halt_thread.start()
        best_result = 0
        while not self.halt_event.is_set():
            result = self.search()
            best_result = result if result > best_result else best_result
            time.sleep(0.5)
        return best_result

    def search(self):
        val = random.randrange(0, 10000)
        print 'searching for something; found {}'.format(val)
        return val

print StochasticSearch().find_best_result(3)

Answer 4

You need an exit condition, or the program will run forever (or until it runs out of memory). Add one yourself.