python - 我如何使用 Selenium 的等待？

Question

我在弄清楚如何使用 Selenium 的等待函数时遇到了麻烦。我想做的是检查一个元素是否存在，如果存在，它将打印一条语句。这是我的代码:

from selenium import webdriver
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.common.exceptions import TimeoutException

browser = webdriver.Firefox()
browser.get("http://google.com")
delay = 3 # seconds
try:
    WebDriverWait(browser, delay).until(EC.presence_of_element_located(browser.find_element_by_xpath('//*[@id="hplogo"]')))
    print ("Page is ready!")
except TimeoutException:
    print ("Loading took too much time!")

当前代码给我以下错误:

Traceback (most recent call last):
  File "/Users/John/Documents/waitTest.py", line 10, in <module>
    WebDriverWait(browser, delay).until(EC.presence_of_element_located(browser.find_element_by_xpath('//*[@id="hplogo"]')))
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/selenium/webdriver/support/wait.py", line 71, in until
    value = method(self._driver)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/selenium/webdriver/support/expected_conditions.py", line 59, in __call__
    return _find_element(driver, self.locator)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/selenium/webdriver/support/expected_conditions.py", line 274, in _find_element
    return driver.find_element(*by)
TypeError: find_element() argument after * must be a sequence, not WebElement

Answer 1

预期条件 expects要传入的元组，其中第一项是定位器的类型(By 常量)，第二项是定位器的值:

from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC    

wait = WebDriverWait(browser, 10)
wait.until(EC.presence_of_element_located((By.XPATH, '//*[@id="hplogo"]')))

请注意，在您的情况下 By.ID 会更简单:

wait.until(EC.presence_of_element_located((By.ID, 'hplogo')))