在Python 2.7中每n秒循环执行一次函数时的初始延迟

Question

I would like to loop the function "logger" every second, ideally start and stop at certain times of the day too, however I haven't worked out the best way to do that yet. I've noticed in the log file that there's a delay between the first and second entry when printing the data. How do I solve this problem?

[u'(LON:SXX)'] - [u'14.38'] - [u'3.88M/6.72M'] - 12:12:36

[u'(LON:SXX)'] - [u'14.38'] - [u'3.88M/6.72M'] - 12:12:43

[u'(LON:SXX)'] - [u'14.38'] - [u'3.88M/6.72M'] - 12:12:44

[u'(LON:SXX)'] - [u'14.38'] - [u'3.88M/6.72M'] - 12:12:45

from selenium.webdriver.firefox import webdriver
from datetime import datetime
import time

starttime=time.time()

driver = webdriver.WebDriver()
driver.get('https://www.google.co.uk/finance?q=LON:SXX') 

def logger():
    with open("log.txt", "a") as f:
        # get the current price & time
        tme = datetime.now().strftime('%H:%M:%S')
        current_price = [price.text for price in driver.find_elements_by_xpath('//*[@id="price-panel"]/div[1]/span') if price.text]
        volume = [vol.text for vol in driver.find_elements_by_xpath('/html/body/div[1]/div/div[3]/div[2]/div/div[2]/div/div/div[2]/div[2]/div[1]/div[2]/div[1]/table[1]/tbody/tr[4]/td[2]') if vol.text]
        symbol = [sym.text for sym in driver.find_elements_by_xpath('/html/body/div/div/div[3]/div[1]/div/div[2]/div[2]/span') if sym.text]
        f.write ("%s - %s - %s - %s \n" % (symbol, current_price, volume, tme))
        f.close

while True:
    logger()
    time.sleep(1.0 - ((time.time() - starttime) % 1.0))

Answer 1

You may choose one of this: - use your OS crontab, - use python crontab module - use a scheduler module

Please see bellow your code example modified to use the python apscheduler module: https://apscheduler.readthedocs.org/en/latest/

from selenium.webdriver.firefox import webdriver
from datetime import datetime
import time

#to install 'apscheduler' use this command 'pip install apscheduler'
from apscheduler.scheduler import Scheduler

#init the scheduler
sched = Scheduler()


starttime=time.time()

driver = webdriver.WebDriver()
driver.get('https://www.google.co.uk/finance?q=LON:SXX') 

#here we are decor the logger function 

@sched.interval_schedule(seconds=1)
def logger():
    with open("log.txt", "a") as f:
        # get the current price & time
        tme = datetime.now().strftime('%H:%M:%S')
        current_price = [price.text for price in driver.find_elements_by_xpath('//*[@id="price-panel"]/div[1]/span') if price.text]
        volume = [vol.text for vol in driver.find_elements_by_xpath('/html/body/div[1]/div/div[3]/div[2]/div/div[2]/div/div/div[2]/div[2]/div[1]/div[2]/div[1]/table[1]/tbody/tr[4]/td[2]') if vol.text]
        symbol = [sym.text for sym in driver.find_elements_by_xpath('/html/body/div/div/div[3]/div[1]/div/div[2]/div[2]/span') if sym.text]
        f.write ("%s - %s - %s - %s \n" % (symbol, current_price, volume, tme))
        f.close


sched.start()