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How to find_element_by_link_text while having: NoSuchElement Exception?

由 血红的双手。 提交于 2019-12-01 09:38:52

It happened to me before that the find_element_by_link_text method sometimes works and sometimes doesn't work; even in a single case. I think it's not a reliable way to access elements; the best way is to use find_element_by_id.

But in your case, as I visit the page, there is no id to help you. Still you can try find_elements_by_xpath in 3 ways:

1- Accessing title: find_element_by_xpath["//a[contains(@title = 'T430')]"]

2- Accessing text: find_element_by_xpath["//a[contains(text(), 'T430')]"]

3- Accessing href: find_element_by_xpath["//a[contains(@href = 'http://www.thedostore.com/laptops/thinkpad-laptops/thinkpad-t430-u-black-627326q.html')]"].

Hope it helps.

From viewing the source of the page that you provided a link to, it seems you are using an incorrect selector.

You should use instead find_elements_by_link_text(u'text here')[0] to select the first occurrence instead as there seems to be the potential for multiple links with the same link text.

So instead of:

self.assertEqual("Thinkpad Edge E530 (Black)", driver.find_element_by_link_text("Thinkpad Edge E530 (Black)").text)

You should use:

self.assertEqual("Thinkpad Edge E530 (Black)", driver.find_elements_by_link_text("Thinkpad Edge E530 (Black)")[0].text)
kenorb

NoSuchElementException is thrown when the element could not be found.

If you encounter this exception, please check the followings:

  • Check your selector used in your find_by...
  • Element may not yet be on the screen at the time of the find operation.

If webpage is still loading, check for selenium.webdriver.support.wait.WebDriverWait() and write a wait wrapper to wait for an element to appear.

Troubleshooting and code samples

You can add breakpoint just before your failing line pdb.set_trace() (don't forget to import pdb), then run your test and once your debugger stops, then do the following tests.

  1. You could try:

    driver.find_element_by_xpath(u'//a[text()="Foo text"]')

    instead. This is more reliable test, so if this would work, use it instead.

  2. If above won't help, please check if your page has been loaded properly via:

    (Pdb) driver.execute_script("return document.readyState")
'complete'

    Sometimes when the page is not loaded, you're actually fetching the elements from the old page. But even though, readyState could still indicate the state of the old page (especially when using click()). Here is how this is explained in this blog:

    Since Selenium webdriver has become more advanced, clicks are much more like "real" clicks, which has the benefit of making our tests more realistic, but it also means it's hard for Selenium to be able to track the impact that a click has on the browsers' internals -- it might try to poll the browser for its page-loaded status immediately after clicking, but that's open to a race condition where the browser was multitasking, hasn't quite got round to dealing with the click yet, and it gives you the .readyState of the old page.

  3. If you think this is happening because the page wasn't loaded properly, the "recommended" (however still ugly) solution is an explicit wait:

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

old_value = browser.find_element_by_id('thing-on-old-page').text
browser.find_element_by_link_text('my link').click()
WebDriverWait(browser, 3).until(
    expected_conditions.text_to_be_present_in_element(
        (By.ID, 'thing-on-new-page'),
        'expected new text'
    )
)

    The naive attempt would be something like this:

    def wait_for(condition_function):
    start_time = time.time()
    while time.time() < start_time + 3:
        if condition_function():
            return True
        else:
            time.sleep(0.1)
    raise Exception(
        'Timeout waiting for {}'.format(condition_function.__name__)
    )


def click_through_to_new_page(link_text):
    browser.find_element_by_link_text('my link').click()

    def page_has_loaded():
        page_state = browser.execute_script(
            'return document.readyState;'
        ) 
        return page_state == 'complete'

    wait_for(page_has_loaded)

    Another, better one would be (credits to @ThomasMarks):

    def click_through_to_new_page(link_text):
    link = browser.find_element_by_link_text('my link')
    link.click()

    def link_has_gone_stale():
        try:
            # poll the link with an arbitrary call
            link.find_elements_by_id('doesnt-matter') 
            return False
        except StaleElementReferenceException:
            return True

    wait_for(link_has_gone_stale)

    And the final example includes comparing page ids as below (which could be bulletproof):

    class wait_for_page_load(object):

    def __init__(self, browser):
        self.browser = browser

    def __enter__(self):
        self.old_page = self.browser.find_element_by_tag_name('html')

    def page_has_loaded(self):
        new_page = self.browser.find_element_by_tag_name('html')
        return new_page.id != self.old_page.id

    def __exit__(self, *_):
        wait_for(self.page_has_loaded)

    And now we can do:

    with wait_for_page_load(browser):
    browser.find_element_by_link_text('my link').click()

    Above code samples are from Harry's blog.

  4. Here is the version proposed by Tommy Beadle (by using staleness approach):

    import contextlib
from selenium.webdriver import Remote
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support.expected_conditions import staleness_of

class MyRemote(Remote):
    @contextlib.contextmanager
    def wait_for_page_load(self, timeout=30):
        old_page = self.find_element_by_tag_name('html')
        yield
        WebDriverWait(self, timeout).until(staleness_of(old_page))

  5. If you think it isn't about page load, double check if your element isn't in iframe or different window. If so, you've to switch to it first. To check list of available windows, run: driver.window_handles.

Solution posted by OP:

Hack 1: Instead of identifying the element as a text-link, I identified the "bigger frame" in which this element was present. itemlist_1 = driver.find_element_by_css_selector("li.item.first").text This will give the whole item along with the name, price and detail (and the unwanted add to cart and compare"

See the attached image for more .

Hack 2: I found that the "Buy Now" which was an image element with xPath (driver.find_element_by_xpath("//div[@id='subseries']/div[2]/div/p[3]/a").click() , in the code above) , could be made to click/identified faster if I added the following line, before finding this by xpath. I think this sort of narrows down where the Webdriver is looking for an element. This is what I added " driver.find_element_by_css_selector("#subseries").text"

This must have decreased my wait by at least 20 seconds, on that page .Hope that helps.

标签
python
xpath
selenium-webdriver
css-selectors
webautomation
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