Why selenium dont find tag and class

I recently started using selenium and I can’t solve one problem. When I use find_element_by_tag(class)_name or _css_selector raise error:

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

But the element I’m looking for exists.

For example:

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')

Output:

[WDM] - Current google-chrome version is 85.0.4183
 
[WDM] - Get LATEST driver version for 85.0.4183
[WDM] - Driver [C:Usersvladv.wdmdriverschromedriverwin3285.0.4183.87chromedriver.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:UsersvladvAppDataLocalProgramsPythonPython37libsite-packagesseleniumwebdriverremotewebdriver.py", line 564, in find_element_by_class_name
    return self.find_element(by=By.CLASS_NAME, value=name)
  File "C:UsersvladvAppDataLocalProgramsPythonPython37libsite-packagesseleniumwebdriverremotewebdriver.py", line 978, in find_element
    'value': value})['value']
  File "C:UsersvladvAppDataLocalProgramsPythonPython37libsite-packagesseleniumwebdriverremotewebdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "C:UsersvladvAppDataLocalProgramsPythonPython37libsite-packagesseleniumwebdriverremoteerrorhandler.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)

But if I want to find “navbar-brand” class, I can do it. What’s the problem?

And if I use find_elements, return empty list.

P.S If somebody can advise some useful material for studying selenium it’ll be very helpful.

Answer

As per the documentation of selenium.webdriver.common.by implementation:

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

    CLASS_NAME = 'class name'
    

So, using find_element_by_class_name() you won’t be able to pass multiple class names. Passing multiple classes you will face an error.

---

Solution

To locate the element you can use either of the following Locator Strategies:

• Using css_selector:

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

• Using xpath:

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

Ideally, to locate the element you need to induce WebDriverWait for the visibility_of_element_located() and you can use either of the following Locator Strategies:

• Using CSS_SELECTOR:

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

• Using XPATH:

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

• Note : You have to add the following imports :

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

References

You can find a couple of relevant detailed discussions in:

• Invalid selector: Compound class names not permitted error using Selenium