def opsite(siteli, tsl=0):
    """
    open a list of websites.
    siteli must be a list, each element of which is one of the websites that you want to open in one single web browser.
    """
    import time
    import numpy as np
    from selenium import webdriver
    osite = webdriver.Chrome()
    n = 1
    for i in siteli:
        osite.get(i)
        time.sleep(tsl * np.random.rand() + 0.002)
        osite.execute_script('window.open()')
        handles = osite.window_handles
        osite.switch_to.window(handles[n])
        n += 1
    osite.close()
    osite.switch_to.window(handles[0])
