Element Not Attached to page document when iterating through web elements

Question

I am trying to iterate clicking through the North American cities in the Uber Movement data.

I have setup Python code to select the table of all cities (cities_table), make it into a list, and identify the button for each city to be clicked (the button has a tag name 'a').

My problem is that I am able to select the first city in the table (Atlanta), but when I try to go back to the page with the table of all cities I do not manage to click on the next city on the list, which should be Boston.

After I successfully enter the Atlanta page, I setup a driver.back() to go back to the cities table, but when trying to move on to the next item on the list, I get the following error message:

Message: stale element reference: element is not attached to the page document

How can I correctly click on a city, go back to the cities table page and click on the NEXT item?

Here is my code so far:

# Load Chrome driver and movement.uber.com/cities website
PATH = 'C:\Program Files (x86)\chromedriver.exe'
driver = webdriver.Chrome(PATH)
driver.get('https://movement.uber.com/cities?lang=en-US')

# City loop
cities_table = driver.find_element_by_xpath('/html/body/div[1]/div[1]/div[1]/div[2]/div[1]/div')
cities = cities_table.find_elements_by_tag_name('div')
for city in cities:
    city = city.find_element_by_tag_name('a') # Buttons have tags "a"
    city.click()
    time.sleep(3)
    driver.back()

Full error message below:

StaleElementReferenceException            Traceback (most recent call last)
<ipython-input-25-a148ef184a6b> in <module>
      6 cities = cities_table.find_elements_by_tag_name('div')
      7 for city in cities:
----> 8     city = city.find_element_by_tag_name('a') # Buttons have tags "a"
      9     city.click()
     10     time.sleep(3)

~\AppData\Roaming\Python\Python37\site-packages\selenium\webdriver\remote\webelement.py in find_element_by_tag_name(self, name)
    303             element = element.find_element_by_tag_name('h1')
    304         """
--> 305         return self.find_element(by=By.TAG_NAME, value=name)
    306 
    307     def find_elements_by_tag_name(self, name):

~\AppData\Roaming\Python\Python37\site-packages\selenium\webdriver\remote\webelement.py in find_element(self, by, value)
    657 
    658         return self._execute(Command.FIND_CHILD_ELEMENT,
--> 659                              {"using": by, "value": value})['value']
    660 
    661     def find_elements(self, by=By.ID, value=None):

~\AppData\Roaming\Python\Python37\site-packages\selenium\webdriver\remote\webelement.py in _execute(self, command, params)
    631             params = {}
    632         params['id'] = self._id
--> 633         return self._parent.execute(command, params)
    634 
    635     def find_element(self, by=By.ID, value=None):

~\AppData\Roaming\Python\Python37\site-packages\selenium\webdriver\remote\webdriver.py in execute(self, driver_command, params)
    319         response = self.command_executor.execute(driver_command, params)
    320         if response:
--> 321             self.error_handler.check_response(response)
    322             response['value'] = self._unwrap_value(
    323                 response.get('value', None))

~\AppData\Roaming\Python\Python37\site-packages\selenium\webdriver\remote\errorhandler.py in check_response(self, response)
    240                 alert_text = value['alert'].get('text')
    241             raise exception_class(message, screen, stacktrace, alert_text)
--> 242         raise exception_class(message, screen, stacktrace)
    243 
    244     def _value_or_default(self, obj, key, default):

StaleElementReferenceException: Message: stale element reference: element is not attached to the page document
  (Session info: chrome=84.0.4147.89)

Answer 1

This error occurs because you are getting the reference of a dom element which no longer exists. Every time a page is reloaded or refreshed, or the dom has somewhat changed, every reference you have previously obtained is useless.

So, in order to work, you have to keep a reference of what you have already processed, and renew your dom reference every time the page changes.

# City loop

managed_cities = []
while True:
    cities_table = driver.find_element_by_xpath('/html/body/div[1]/div[1]/div[1]/div[2]/div[1]/div')
    cities = cities_table.find_elements_by_tag_name('div')
    for city in cities:
        # Here you have to find and ID or some unique text that identifies the
        # already processed city in order to skip it
        if city.text in managed_cities:
            continue

        city = city.find_element_by_tag_name('a') # Buttons have tags "a"
        city.click()
        time.sleep(3)
        driver.back()
        break

    # Now, if you have managed all the cities, you can exit from the while
    # otherwise, keep loop until all cities have been processed
    if len(managed_cities) == len(cities):
        break