Selenium with Python: Stale Element Reference Exception

Question

Working from Test Driven Development with Python, and I'm currently encountering a 'StaleElementReferenceException' when running the functional test immediately after migration. Here's the full text of the error:

ERROR: test_start_and_retrieve_list (__main__.NewVisitorTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "functional_tests.py", line 53, in test_start_and_retrieve_list
    rows = table.find_elements_by_tag_name('tr')
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webelement.py", line 237, in find_elements_by_tag_name
    return self.find_elements(by=By.TAG_NAME, value=name)
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webelement.py", line 527, in find_elements
    {"using": by, "value": value})['value']
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webelement.py", line 493, in _execute
    return self._parent.execute(command, params)
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webdriver.py", line 256, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/errorhandler.py", line 194, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.StaleElementReferenceException: Message: The element reference of <table id="id_list_table"> stale: either the element is no longer attached to the DOM or the page has been refreshed


----------------------------------------------------------------------
Ran 1 test in 8.735s

FAILED (errors=1)

Here's the test:

from selenium import webdriver
from selenium.webdriver.common.keys import Keys
import unittest

class NewVisitorTest(unittest.TestCase): 

    def setUp(self):
        self.browser = webdriver.Firefox()
        self.browser.implicitly_wait(3)

    def tearDown(self):
        self.browser.close()

    def check_for_row(self, row_text):
        table = self.browser.find_element_by_id('id_list_table')
        rows = table.find_elements_by_tag_name('tr')
        self.assertIn(row_text, [row.text for row in rows])

    def test_start_and_retrieve_list(self):    
        self.browser.get('http://localhost:8000')

        self.assertIn('To-Do', self.browser.title)
        header_text = self.browser.find_element_by_tag_name('h1').text
        self.assertIn('To-Do', header_text)

        inputbox = self.browser.find_element_by_id('id_new_item')
        self.assertEqual(
            inputbox.get_attribute('placeholder'),
            'Enter a to-do item'
        )

        inputbox.send_keys('Buy peacock feathers')

        inputbox.send_keys(Keys.ENTER)
        self.check_for_row('1: Buy peacock feathers')

        inputbox = self.browser.find_element_by_id('id_new_item')
        inputbox.send_keys('Use peacock feathers to make a fly')
        inputbox.send_keys(Keys.ENTER)

        table = self.browser.find_element_by_id('id_list_table')
        rows = table.find_elements_by_tag_name('tr')
        self.check_for_row('1: Buy peacock feathers')
        self.check_for_row('2: Use peacock feathers to make a fly')

        self.fail('Finish the test!')

if __name__ == '__main__':
    unittest.main(warnings='ignore')

How do I configure the test to prevent this? Selenium's own page says this issue can occur when the page refreshes, but this is a necessary part of the application logic as it's configured so far.

Answer 1

Add these imports:

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

Change these lines

inputbox.send_keys(Keys.ENTER)
self.check_for_row('1: Buy peacock feathers')

to:

inputbox.send_keys(Keys.ENTER)

WebDriverWait(self.browser, 10).until(
            expected_conditions.text_to_be_present_in_element(
                (By.ID, 'id_list_table'), 'Buy peacock feathers'))

self.check_for_row('1: Buy peacock feathers')

This replaces the time.sleep(1) with something more "reasonable"