How to find_element_by_link_text while having: NoSuchElement Exception?

问题

This question has been asked over and over again - and in-spite of trying all the hacks I still can't seem to figure out what's wrong.

I tried increasing the implicitly_wait to 30 (and even increased it upto 100) - yet it did not work.

Use case -: I am trying to create a list that wil populate all the items in the page here, as a base case - and I intend to bind this to a mini-module that I already have with scrapy which has all (pages with similar web elements) crawled links - so essentially will be building the whole pipeline, post I am done with this.

###My source code - generated via Selenium IDE, exported to a Python webdriver and manipulated a little later ###

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import Select
from selenium.common.exceptions import NoSuchElementException
from selenium.webdriver.support.wait import WebDriverWait
import unittest, time, re

class Einstein(unittest.TestCase):
    def setUp(self):
        self.driver = webdriver.Firefox()
        self.driver.implicitly_wait(30)
        self.base_url = "http://shopap.lenovo.com/in/en/laptops/"
        self.verificationErrors = []
        self.accept_next_alert = True

    def test_einstein(self):
        driver = self.driver
        driver.get(self.base_url)
        print driver.title
        driver.find_element_by_link_text("T430").click()
        print driver.title
#       driver.find_element_by_xpath("id('facetedBrowseWrapper')/div/div/div[1]/div[2]/ul[1]/li[1]/a").click()
        driver.find_element_by_xpath("//div[@id='subseries']/div[2]/div/p[3]/a").click()
        print driver.title
       # driver.find_element_by_xpath("//div[@id='subseries']/div[2]/div/p[3]/a").click()
        try: self.assertEqual("Thinkpad Edge E530 (Black)", driver.find_element_by_link_text("Thinkpad Edge E530 (Black)").text)
        except AssertionError as e: self.verificationErrors.append(str(e))
       # Everything ok till here

        #**THE CODE FAILS HERE**#
        laptop1 = driver.find_element_by_link_text("Thinkpad Edge E530 (Black)").text
        print laptop1
        price1 = driver.find_element_by_css_selector("span.price").text
        print price1
        detail1 = self.is_element_present(By.CSS_SELECTOR, "div.desc.std")
        print detail1

            def is_element_present(self, how, what):
        try: self.driver.find_element(by=how, value=what)
        except NoSuchElementException, e: return False
        return True

    def is_alert_present(self):
        try: self.driver.switch_to_alert()
        except NoAlertPresentException, e: return False
        return True

    def close_alert_and_get_its_text(self):
        try:
            alert = self.driver.switch_to_alert()
            alert_text = alert.text
            if self.accept_next_alert:
                alert.accept()
            else:
                alert.dismiss()
            return alert_text
        finally: self.accept_next_alert = True

    def tearDown(self):
        self.driver.quit()
        self.assertEqual([], self.verificationErrors)

if __name__ == "__main__":
    unittest.main()


Errors & output :
ekta@ekta-VirtualBox:~$ python einstein.py
Laptops & Ultrabooks | Lenovo (IN)
ThinkPad T430 Laptop PC for Business Computing | Lenovo (IN)
Buy Lenovo Thinkpad Laptops | Lenovo Thinkpad Laptops Price India
E
======================================================================
ERROR: test_einstein (__main__.Einstein)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "einstein.py", line 27, in test_einstein
    try: self.assertEqual("Thinkpad Edge E530 (Black)", driver.find_element_by_link_text("Thinkpad Edge E530 (Black)").text)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py", line 246, in find_element_by_link_text
    return self.find_element(by=By.LINK_TEXT, value=link_text)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py", line 680, in find_element
    {'using': by, 'value': value})['value']
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/webdriver.py", line 165, in execute
    self.error_handler.check_response(response)
  File "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/remote/errorhandler.py", line 158, in check_response
    raise exception_class(message, screen, stacktrace)
NoSuchElementException: Message: u'Unable to locate element: {"method":"link text","selector":"Thinkpad Edge E530 (Black)"}' ; Stacktrace: 
    at FirefoxDriver.prototype.findElementInternal_ (file:///tmp/tmphli5Jg/extensions/fxdriver@googlecode.com/components/driver_component.js:8444)
    at fxdriver.Timer.prototype.setTimeout/<.notify (file:///tmp/tmphli5Jg/extensions/fxdriver@googlecode.com/components/driver_component.js:386) 

----------------------------------------------------------------------
Ran 1 test in 79.348s

FAILED (errors=1)

Questions & comments:

If you are answering this question - please mention why this specific "find_element_by_link_text" does not work.
(Very Basic) In the GUI of my selenium IDE -> Show all available commands - why dont I see the css (find_element_by_css_selector) for all the web elements - is there a way to force feed an element to be read as a CSS selector ?
In case you suggest using some other locator - please mention if that will be consistent way to fetch elements, given (1)
Does assert work to capture the exceptions and "move on" - since even after trying "verify" , "assert" loops, I still cant fetch this "find_element_by_link_text"
I tried using Xpath to build this "element" , but in the view Xpath (in firefox) - I see nothing, to clue why that happens (Of course I removed the namespace ":x" )

Other things I tried apart from implicity_wait(30):

find_element_by_partial_link(“Thinkpad”) and appending Unicode to this (wasn’t sure if it was reading the brackets ( , driver.find_element_by_link_text(u"Thinkpad Edge E530 (Black)").text, still did not work.

回答1:

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.

回答2:

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)

回答3:

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.

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.
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.

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.

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))

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.

回答4:

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.

来源：https://stackoverflow.com/questions/18023678/how-to-find-element-by-link-text-while-having-nosuchelement-exception

标签

python

xpath

selenium-webdriver

css-selectors

webautomation