finding elements sometimes cause error TypeError: object of type 'NoneType' has no len() or KeyError: 0

[ombre42]

Sometimes the underlying call to Selenium methods such as find_elements_by_xpath return a dict with value=None. This None value is propagated all the way up to _element._element_find, where len() is used to see how many elements were found. This will cause Wait Until Page Contains Element to fail immediately, since you can't use len on None.
Unfortunately I don't have a simple test/page to reproduce, but here's a log from executing Selenium2Library.Wait Until Page Contains Element id=delivery_date_select, 1m

08:31:43.590 DEBUG POST http://127.0.0.1:50341/session/a61ed99c-c9ed-4e49-9045-8b3c7724eeac/elements {"using": "id", "sessionId": "a61ed99c-c9ed-4e49-9045-8b3c7724eeac", "value": "delivery_date_select"}
08:31:44.160 DEBUG POST http://127.0.0.1:50341/session/a61ed99c-c9ed-4e49-9045-8b3c7724eeac/elements {"using": "id", "sessionId": "a61ed99c-c9ed-4e49-9045-8b3c7724eeac", "value": "delivery_date_select"}
08:31:44.573 FAIL TypeError: object of type 'NoneType' has no len()
08:31:44.574 DEBUG Traceback (most recent call last):
File "", line 2, in wait_until_page_contains_element
File "C:\apps\Python27\lib\site-packages\Selenium2Library\keywords\keywordgroup.py", line 12, in _run_on_failure_decorator
return method(_args, *_kwargs)
File "C:\apps\Python27\lib\site-packages\Selenium2Library\keywords_waiting.py", line 63, in wait_until_page_contains_element
self._wait_until(timeout, error, self._is_element_present, locator)
File "C:\apps\Python27\lib\site-packages\Selenium2Library\keywords_waiting.py", line 71, in _wait_until
while not function(*args):
File "C:\apps\Python27\lib\site-packages\Selenium2Library\keywords_element.py", line 593, in _is_element_present
return (self._element_find(locator, True, False, tag=tag) != None)
File "C:\apps\Python27\lib\site-packages\Selenium2Library\keywords_element.py", line 515, in _element_find
if len(elements) == 0: return None

[ombre42]

Not sure if it helps but this is happening with the IE driver, and in many versions of Selenium.
Best I can tell, the driver is violating the JsonWireProtocol because the return type for /session/:sessionId/elements is supposed to be {Array.<{ELEMENT:string}>}.

[Johnz86]

This happens a lot for me, when I use webdriver and try testing on IE9.

[ombre42]

I was thinking of submitting a patch that just converts None into [], which will allow wait until page contains to work again. I think an INFO level event should be logged when that happens.

[ombre42]

Fix submitted as pull request in issue #151

[ombre42]

This is still occurring with Selenium 2.31 & IEDriverServer 2.32.3.0
A bug has been reported upstream in the Selenium project.

Here is what the failure looks like if the find returns a dict:
06:00:58.788 DEBUG POST http://127.0.0.1:4843/session/283cb180-65d7-4d58-8431-fee1a3b4fc8f/elements {"using": "xpath", "sessionId": "283cb180-65d7-4d58-8431-fee1a3b4fc8f", "value": "id('scriptId')[.='Enter the DNIS number that shows on your phone display']"}
06:01:01.960 FAIL KeyError: 0
06:01:01.960 DEBUG Traceback (most recent call last):
File "C:\Jenkins\workspace\Apollo_Login\Lib\Selenium2LibraryExt.py", line 152, in wait_until_element_visible
lib._wait_until(timeout, error, lib._is_visible, locator)
File "C:\Jenkins\workspace\Apollo_Login\Lib\Selenium2LibraryExt.py", line 328, in _wait_until_ignoring
if function(*args): return
File "c:\Apps\Python27\lib\site-packages\Selenium2Library\keywords_element.py", line 580, in _is_visible
element = self._element_find(locator, True, False)
File "c:\Apps\Python27\lib\site-packages\Selenium2Library\keywords_element.py", line 542, in _element_find
return elements[0]

Here is some captured JSON that from a different run that had the same failure:
{"sessionId":"4cadce81-ec77-477f-83de-d3b29ffb84f4","status":0,"value":{"":null}}

[ombre42]

Actually not sure if the TypeError is still happening but the KeyError definitely is and that is also addressed in my pull request.

[emanlove]

This issue was fixed under Selenium2Library version 1.3 by #172.