python - 为什么 Selenium 找不到标签和类

Question

我最近开始使用 Selenium ，但我无法解决一个问题。当我使用 find_element_by_tag(class)_name 或 _css_selector 时引发错误:

selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element:

但我正在寻找的元素存在。
例如:

from selenium import webdriver

from webdriver_manager.chrome import ChromeDriverManager

browser = webdriver.Chrome(ChromeDriverManager().install())
url='http://inventwithpython.com/'
browser.get(url)
a = browser.find_element_by_class_name('navbar navbar-toggleable-md')

输出:

[WDM] - Current google-chrome version is 85.0.4183
 
[WDM] - Get LATEST driver version for 85.0.4183
[WDM] - Driver [C:\Users\vladv\.wdm\drivers\chromedriver\win32\85.0.4183.87\chromedriver.exe] found in cache
Traceback (most recent call last):
  File "C:/Users/vladv/PycharmProjects/untitled1/черновик.py", line 14, in <module>
    a = browser.find_element_by_class_name('navbar navbar-toggleable-md')
  File "C:\Users\vladv\AppData\Local\Programs\Python\Python37\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 564, in find_element_by_class_name
    return self.find_element(by=By.CLASS_NAME, value=name)
  File "C:\Users\vladv\AppData\Local\Programs\Python\Python37\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 978, in find_element
    'value': value})['value']
  File "C:\Users\vladv\AppData\Local\Programs\Python\Python37\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "C:\Users\vladv\AppData\Local\Programs\Python\Python37\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element: {"method":"css selector","selector":".navbar navbar-toggleable-md"}
  (Session info: chrome=85.0.4183.102)

但是如果我想找到“navbar-brand”类，我可以做到。
有什么问题？
如果我使用 find_elements，则返回空列表。
P.S 如果有人可以建议一些有用的 Material 来研究 Selenium ，那将非常有帮助。

Answer 1

根据 selenium.webdriver.common.by 的文档执行:

class selenium.webdriver.common.by.By
    Set of supported locator strategies.

    CLASS_NAME = 'class name'
    

因此，使用 find_element_by_class_name()您将无法传递多个类名。
传递多个类，您将面临错误。

解决方案
要定位元素，您可以使用以下任一方法 Locator Strategies :

使用 css_selector :

element = driver.find_element_by_css_selector("nav.navbar.navbar-toggleable-md")

使用 xpath :

element = driver.find_element_by_xpath("//nav[@class='navbar navbar-toggleable-md']")

理想情况下，要定位需要诱导的元素 WebDriverWait为 visibility_of_element_located()您可以使用以下任一 Locator Strategies :

使用 CSS_SELECTOR :

element = WebDriverWait(driver, 20).until(EC.visibility_of_element_located((By.CSS_SELECTOR, "nav.navbar.navbar-toggleable-md")))

使用 XPATH :

element = WebDriverWait(driver, 20).until(EC.visibility_of_element_located((By.XPATH, "//nav[@class='navbar navbar-toggleable-md']")))

备注 :您必须添加以下导入:

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

引用
您可以在以下位置找到一些相关的详细讨论:

Invalid selector: Compound class names not permitted error using Selenium