Non blocking wait in selenium using Python

Prerequisite : Browser Automation Using Selenium

When we want to do web automation, we require to wait for some javascript elements to load before we perform some action. For that matter, generally people use

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time.sleep(in_seconds)

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which is a blocking call.



By blocking call I mean, it waits or rather makes the program sleep for mentioned seconds no matter what happens. This isn’t a good idea as it increases the latency by making the program effectively slower.

The possible solution to this is to wait until a element appears and not wait for more than that.
Pre-requisites: Python installed and Selenium installed as package along with the web driver (.exe file)

For Python Web Automation with Selenium, this can be achieved as follows:

Let’s say you want to login on GeeksForGeeks through web automation and fill the login credentials as soon as username and password elements are visible on the web page and not wait until the whole page is loaded.

Step1:

You configure the webdriver as follows:

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from selenium import webdriver
  
options = webdriver.ChromeOptions()
options.add_argument("--start-maximized")
options.add_argument("disable-infobars")
  
chrome = webdriver.Chrome(the_path_of_webdriver_which_is_an_exe,
                          chrome_options = options, service_args =['--ignore-ssl-errors = true'])
  
username = 'something'
password = 'anything'
username_xpath = '//*[@id ="luser"]'
password_xpath = '//*[@id ="password"]'
sign_in_xpath = '//*[@id ="Login"]/button'
  
chrome.get(login_uri)

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Here I’ve used chrome web driver which would start maximised (full window) with no infobars i.e it won’t say that chrome is being controlled by automation code and load the sign page of GFG without any hassle.

Do Note that in order to find the xpath of these elements you need to get into the developer mode and inspect these elements.

Step 2:

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# return True if element is visible within 30 seconds, otherwise False
def is_visible(locator, timeout = 30):
    try:
        ui.WebDriverWait(chrome, timeout).until(EC.visibility_of_element_located((By.XPATH, locator)))
        return True
    except TimeoutException:
        return False

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The above function is_visible is facilitator of the non blocking call we intend to discuss here.
Explanation:
1) locator – the xpath of the element
2) timeout – until when to wait for the element to appear (beacuse we don’t want to wait forever)
3) chrome – the webdriver object we initialized earlier
4) It utilizes the inbuild utlity of ui to make the web driver wait until the element is visible (identified by xpath)
5) if it does appear within the timeout it returns True else False


Step 3:

This is how we utilize the function:

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if not is_visible(username_xpath): raise RuntimeError("Something went wrong with the username field :(")
username_field = chrome.find_element_by_xpath(username_xpath)
username_field.send_keys(username)
  
if not is_visible(password_xpath): raise RuntimeError("Something went wrong with the password field :(")
password_field = chrome.find_element_by_xpath(password_xpath)
password_field.send_keys(password)
  
if not is_visible(sign_in_xpath): raise RuntimeError("Something went wrong with the sign in field :(")
sign_in_btn = chrome.find_element_by_xpath(sign_in_xpath)
sign_in_btn.click()

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Here we call the is_visible function and pass the xpath of username, password and sign_in button respectively and wait for the element to appear withing timeout (here 30s). If not visible then we raise an RuntimeError with appropriate message.

If it appears anytime earlier than 30s it proceeds and find the element by xpath (as now it is visible on the webpage so this call wouldn’t throw exception error).

We then send the data and click on sign in and you can enjoy learning on GFG without any blocking call 😛



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