Ошибки selenium python

Exceptions that may happen in all the webdriver code.

Exceptions

exception selenium.common.exceptions.ElementClickInterceptedException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

The Element Click command could not be completed because the element
receiving the events is obscuring the element that was requested to be
clicked.

exception selenium.common.exceptions.ElementNotInteractableException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when an element is present in the DOM but interactions with that
element will hit another element due to paint order.

exception selenium.common.exceptions.ElementNotSelectableException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when trying to select an unselectable element.

For example, selecting a ‘script’ element.

exception selenium.common.exceptions.ElementNotVisibleException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when an element is present on the DOM, but it is not visible, and
so is not able to be interacted with.

Most commonly encountered when trying to click or read text of an
element that is hidden from view.

exception selenium.common.exceptions.ImeActivationFailedException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when activating an IME engine has failed.

exception selenium.common.exceptions.ImeNotAvailableException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when IME support is not available.

This exception is thrown for every IME-related method call if IME
support is not available on the machine.

exception selenium.common.exceptions.InsecureCertificateException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Navigation caused the user agent to hit a certificate warning, which is
usually the result of an expired or invalid TLS certificate.

exception selenium.common.exceptions.InvalidArgumentException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

The arguments passed to a command are either invalid or malformed.

exception selenium.common.exceptions.InvalidCookieDomainException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when attempting to add a cookie under a different domain than the
current URL.

exception selenium.common.exceptions.InvalidCoordinatesException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

The coordinates provided to an interaction’s operation are invalid.

exception selenium.common.exceptions.InvalidElementStateException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when a command could not be completed because the element is in
an invalid state.

This can be caused by attempting to clear an element that isn’t both
editable and resettable.

exception selenium.common.exceptions.InvalidSelectorException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when the selector which is used to find an element does not
return a WebElement.

Currently this only happens when the selector is an xpath expression
and it is either syntactically invalid (i.e. it is not a xpath
expression) or the expression does not select WebElements (e.g.
“count(//input)”).

exception selenium.common.exceptions.InvalidSessionIdException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Occurs if the given session id is not in the list of active sessions,
meaning the session either does not exist or that it’s not active.

exception selenium.common.exceptions.InvalidSwitchToTargetException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when frame or window target to be switched doesn’t exist.

exception selenium.common.exceptions.JavascriptException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

An error occurred while executing JavaScript supplied by the user.

exception selenium.common.exceptions.MoveTargetOutOfBoundsException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when the target provided to the ActionsChains move() method is
invalid, i.e. out of document.

exception selenium.common.exceptions.NoAlertPresentException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when switching to no presented alert.

This can be caused by calling an operation on the Alert() class when
an alert is not yet on the screen.

exception selenium.common.exceptions.NoSuchAttributeException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when the attribute of element could not be found.

You may want to check if the attribute exists in the particular
browser you are testing against. Some browsers may have different
property names for the same property. (IE8’s .innerText vs. Firefox
.textContent)

exception selenium.common.exceptions.NoSuchCookieException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

No cookie matching the given path name was found amongst the associated
cookies of the current browsing context’s active document.

exception selenium.common.exceptions.NoSuchElementException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when element could not be found.

If you encounter this exception, you may want to check the following:

• Check your selector used in your find_by…
• Element may not yet be on the screen at the time of the find operation,
  (webpage is still loading) see selenium.webdriver.support.wait.WebDriverWait()
  for how to write a wait wrapper to wait for an element to appear.

exception selenium.common.exceptions.NoSuchFrameException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when frame target to be switched doesn’t exist.

exception selenium.common.exceptions.NoSuchShadowRootException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when trying to access the shadow root of an element when it does
not have a shadow root attached.

exception selenium.common.exceptions.NoSuchWindowException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when window target to be switched doesn’t exist.

To find the current set of active window handles, you can get a list
of the active window handles in the following way:

print driver.window_handles

exception selenium.common.exceptions.ScreenshotException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

A screen capture was made impossible.

exception selenium.common.exceptions.SeleniumManagerException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Raised when an issue interacting with selenium manager occurs.

exception selenium.common.exceptions.SessionNotCreatedException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

A new session could not be created.

exception selenium.common.exceptions.StaleElementReferenceException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when a reference to an element is now “stale”.

Stale means the element no longer appears on the DOM of the page.

Possible causes of StaleElementReferenceException include, but not limited to:

• You are no longer on the same page, or the page may have refreshed since the element
  was located.
• The element may have been removed and re-added to the screen, since it was located.
  Such as an element being relocated.
  This can happen typically with a javascript framework when values are updated and the
  node is rebuilt.
• Element may have been inside an iframe or another context which was refreshed.

exception selenium.common.exceptions.TimeoutException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when a command does not complete in enough time.

exception selenium.common.exceptions.UnableToSetCookieException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when a driver fails to set a cookie.

exception selenium.common.exceptions.UnexpectedAlertPresentException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None, alert_text: Optional[str] = None)[source]¶

Thrown when an unexpected alert has appeared.

Usually raised when an unexpected modal is blocking the webdriver
from executing commands.

exception selenium.common.exceptions.UnexpectedTagNameException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Thrown when a support class did not get an expected web element.

exception selenium.common.exceptions.UnknownMethodException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

The requested command matched a known URL but did not match any methods
for that URL.

exception selenium.common.exceptions.WebDriverException(msg: Optional[str] = None, screen: Optional[str] = None, stacktrace: Optional[Sequence[str]] = None)[source]¶

Base webdriver exception.

In the world of automation testing, Selenium is a free and open-source framework used to perform web application testing in web browsers like Chrome, Safari, Firefox, Opera, and Edge. You can write Selenium IDE tests using various programming languages such as Python, Java, JavaScript(Node.js), Kotlin, Ruby, PHP, and C#.

While the advantages of automated testing using Selenium are endless, there are incidences of errors and exceptions that happen regularly in the testing tool (or framework). When a program’s execution is disrupted during run-time, an exception is raised, preventing further instructions from being executed. Runtime errors are raised when you perform an unanticipated operation during runtime.

Exception and error handling is a programming mechanism by which the occurrence of errors and exceptions that halt the execution of a program are responded to by the program to ensure the normal execution of code.

In this blog on handling exceptions in Selenium Python, we will look at the variety of exceptions and errors that can happen when a Selenium test is running. By the end of this blog, you will be able to implement error and exception handling for Selenium automation tests.

So, let’s get started!

Introduction to Errors and Exceptions in Selenium Python

For a program or application to run, a developer must write code that tests every aspect of its functionality. However, the instructions outlined in the code sometimes do not execute as intended.

For QA engineers, the same rule holds when writing code used to test the features and functionality of the applications that have been created to ensure that the application is ready for production and then shipped to the users.

Here is an analogy to help you better understand errors and exceptions in Selenium Python.

Imagine you have a work meeting on Zoom or any online video conference application while at home. During the meeting, the electricity was cut off, which is reported to have affected the whole city. You have no choice but to call off the meeting and wait for the electricity to be reinstated. Akin to this, errors are raised during runtime, and rectifying them is nearly impossible.

In contrast, exceptions are events that raise interruptions while an application runs and can be rectified using exception handling.

Exceptions in Selenium Python are generally classified into two types.

• Checked Exceptions
• Unchecked Exceptions

Checked Exception handling in Selenium is conducted while writing the code. On the other hand, Unchecked Exceptions are raised during runtime and can generate fatal errors compared to the former type of exception.

The class hierarchy of error and exceptions in Selenium Python

You can quickly sharpen your knowledge of exceptions in Selenium Python by reading through this detailed blog on different exceptions in Selenium.

Performing Selenium automated browser testing differs across the ecosystem in which the tests are being carried out. The test scripts may differ depending on the operating systems, browsers, or programming languages they are written in. Therefore, the raised errors andexceptions in Selenium Python may be different. For example, if the browsers don’t have the specified element, Selenium testing of an element property in web browsers may raise exceptions like NoSuchElementException.

To ensure that the applications function correctly and obstruct users’ interactions with the finished product, it is advised that Selenium error and exception handling be used as a standard practice.

Common Exceptions in Selenium Python

According to a recent Stack Overflow developer survey, Python is the fourth most popular programming language among developers.

It offers a robust support system for test automation frameworks and is the most user-friendly and straightforward programming language available.

Errors and exceptions in Selenium Python are common and can occur when writing tests. The exception instances must be derived from a class that inherits from BaseException. If two exception instances do not have a subclass relationship, they are not considered equal despite having the same properties, such as names.

While writing code for the test scripts, the code can run into built-in exceptions, or you can raise exceptions in the code. The interpreter or built-in functions generate the built-in exceptions.

The selenium.common.exceptions package contains the exception classes, which can be imported in the following way.

Syntax: from selenium.common.exceptions import [Exception Name]

An example of an exception being imported is below:

This exception indicates that the website does not contain the attribute of the element being looked for.

Other exceptions in Selenium Python include:

• TimeOutException

When a command does not complete in the time duration set (seconds), this exception is raised or thrown. The wait time can either be implicitly or explicitly defined.

• NoSuchElementException

When an element cannot be found, this exception is raised or thrown. Nonetheless, different factors can lead to this exception being generated:

• The element is not yet in the DOM when the find operation is performed because the page loading is in progress.
• Incorrect element locator is used in the source code.

• ElementNotInteractableException

Such exceptions in Selenium Python is raised whenever an element in the DOM is present but cannot be interacted with.

• ElementNotVisibleException

This exception typically arises when the interaction involves clicking or reading text from an element that is not visible in the DOM.

• StaleElementReferenceException

An outdated or unavailable element in the DOM is referred to as a stale element. A reference to an element that is currently “stale” will raise or throw this exception.

For example, the following reasons could lead to the StaleElementReferenceException exception:

• After the element was located, the page either changed or was refreshed.
• A refreshed context may have contained the element.
• Complete deletion of the referenced web element.

• ElementClickInterceptedException

This exception arises when the element receiving the interaction impedes the element intended to be clicked, thereby preventing the Element Click operation from being performed.

• NoSuchCookieException

This exception will be raised if a cookie with the specified path name is not contained amongst the corresponding cookies of an active document in the current browsing session. To learn more about cookies in Selenium, check out this detailed tutorial on handling cookies in the Selenium WebDriver.

Watch this video to understand how you can handle Cookies and perform different operations like deleting, getting the parameter values, and adding them to Selenium WebDriver using Java.

• InvalidArgumentException

A command with improper or incorrect argument inputs will raise an InvalidArgumentException.

• InvalidElementStateException

This exception is raised when we try to perform an operation that does not apply to an element. For example, if we perform a click operation on a radio button that is disabled, the exception will be raised, and hence the command given cannot be executed.

• NoSuchWindowException

This exception is thrown when the intended window target cannot be found.

If you are a Python programmer looking to make a mark, you can take your career to the next level with the Selenium Python 101 certification from LambdaTest.

Here’s a short glimpse of the Selenium Python 101 certification from LambdaTest:

Handling Errors and Exceptions in Selenium Python

Handling errors and exceptions in Selenium Python are vital when writing production-ready code, since exceptions and errors can arise for different reasons, as discussed earlier.

A prerequisite to writing tests using Selenium Python is to install Python and Selenium on your machine. When using Python for Selenium testing, the default framework used is PyUnit, also known as unittest, which is influenced by JUnit. It functions similarly to other unit testing frameworks.

However, in this blog on handling errors and exceptions in Selenium Python, we will use Pytest, another Python testing framework that supports functions, APIs, and unit testing. It is compatible with the current versions of Python and is easy to configure using the Python Package Manager (pip) command in the terminal.

If you are new to testing using Selenium Python, here is a detailed step-by-step tutorial on how to get started with Selenium Python. You will learn how to configure Python, Selenium, and Pytest on your machine to start automation testing with Selenium. You can learn more about Pytest through this Selenium Pytest tutorial.

Project Setup

For the test project setup, we are using the Visual Studio (VS) Code IDE to write the test scripts. Alternatively, there are other IDEs available, such as Pycharm, Atom, and Sublime Text, that you can use as well.

For the package manager, we will use Poetry, a Python tool that manages and packages the necessary dependencies in a specific virtual environment for your project. You can declare the libraries your project depends on, and it will take care of managing (installing and updating) them.

1. To install Poetry on your local machine’s terminal, please use the following command:
• For Windows

pip install poetry

• For Mac

pip3 install poetry (depends on the Python version you are using).

2. Move to the directory where your project will be contained.



3. To initialize Poetry in the terminal, we use the command poetry init. This command will generate a pyproject.toml configuration file containing the build system requirements for Python projects.



4. We need the following libraries in our project to run Selenium Python tests:
• selenium (v 4.3.0)
• flake8 (v 4.0.1)
• pytest (v 7.1.2)
• pytest-xdist (v 2.5.0)
• autopep8 (v 1.6.0)

The pytest-xdist plugin adds new test execution modes to Pytest, allowing us to run parallel Selenium Python tests. Autopep8 formats the Python code to adhere to the PEP 8 style manual. Flake8 is a great tool that tests your code for errors against the PEP 8 style guide.

5. Adding Selenium:



6. Adding pytest:



7. Adding pytest-xdist.



8. Adding autopep8.



9. Adding flake8.



10. After installing the required dependencies, continue to press Enter, then confirm the generation of the file.
11. The pyproject.toml file contains all the packages that must be installed in the virtual environment.

To install the dependencies mentioned, run the following command to create the pyproject.toml and poetry.lock files in the directory.

A virtual environment (venv) containing the dependencies installed will be automatically created by Poetry. This is important since we do not want to mix Python’s global dependencies with the specific dependencies we require to run the tests in the project.

In our project, we create a folder that will hold the test functions. Let’s call it “seltests”.

Handling Errors and Exceptions on the Cloud Selenium Grid

Now that we have covered the essentials to get started with Python web automation in Selenium, we will look at handling errors and exceptions in Selenium Python on a cloud grid. In this instance, we are using LambdaTest.

LambdaTest is a cloud-based cross browser testing platform that allows you to perform Python automation testing at scale over a cloud Selenium Grid. The unique and fully featured platform offers an online browser farm of 3000+ real browsers across multiple operating systems; thus helping businesses deliver more quality software at a more rapid speed.

You can also Subscribe to the LambdaTest YouTube Channel and stay updated with the latest tutorials around automated browser testing, Selenium testing, Cypress E2E testing, CI/CD, and more.

To get started with LambdaTest, please follow the below-mentioned steps:

1. Register and log in to your LambdaTest account.
2. Move to the LambdaTest Profile Section and copy your username and access key, which will be used to access the Remote Selenium Grid of LambdaTest.
3. You will also need the desired capabilities generated using the LambdaTest Capabilities Generator. You can generate the capabilities needed for the specific test you are carrying out on that page.

We have listed the different types of exceptions in Selenium Python in the blog. Now, we will dig deeper into two common exceptions in Selenium Python when performing automated tests.

NoSuchElementException

A NoSuchElementException is thrown if we attempt to locate any element unavailable on the page (or the DOM).

Scenario 1 (Chrome Browser)

1. Go to the URL link https://www.lambdatest.com/selenium-playground/.
2. Locate an element called “p-10” by its name.
3. Click on the element.

Scenario 2 (Firefox Browser)

1. Go to the URL link https://www.lambdatest.com/selenium-playground/.
2. Locate an element called “level-up” by its name.
3. Click on the element.

Implementation (Scenario 1 on the Chrome Browser):

FileName – test_nosuchelement_google.py

Implementation (Scenario 2 on the Firefox Browser):

FileName – test_nosuchelement_firefox.py

GitHub

Code Execution:

We run the two test scripts using parallel testing, which allows the execution of the same tests simultaneously. To run the test, type the following command in the terminal.

The terminal shows that the test execution failed.

In the LambdaTest Builds dashboard, the failed test executions are displayed.

Code Walkthrough:

We are conducting a joint code walkthrough because the imported Selenium Python libraries used in both test scenarios are identical.

Step 1: Import the necessary Selenium Python classes – pytest, webdriver, sys, By, NoSuchElementException.

We imported pytest, primarily used for unit testing in Selenium Python. Selenium WebDriver is a web framework that enables us to perform cross-browser testing, and in this case, we are using Python to write the test scripts. The By query is based on the find_element() method in Selenium that targets a specific locator.

Step 2: We specify the browser capabilities based on the browser we use to conduct the automated tests in LambdaTest. They are generated using the LambdaTest Capabilities Generator.

Chrome

Firefox

Step 3: We define a function that starts with “test” in which we assign the test methods. You can learn more about it through this blog on Pytest testing using Selenium WebDriver.

Step 4: We then set our LambdaTest username and accesskey to variables we appended to remote_url. This remote URL connects us to the Remote Selenium Grid (@hub.lambdatest.com/wd/hub).

Step 5: We then use the remote_url and browser capabilities to instantiate the corresponding browser (i.e. Chrome or Firefox)

Chrome

Firefox

Step 6: We then get the URL of the website on which we want to locate a specific element. In our test, we try to locate an element by its name and click on it. Once the element had been located and clicked, we quit the test.

Chrome

Firefox

Watch this video to learn exception handling in Selenium, which covers different types of exceptions and how to handle them using various methods.

NoSuchElementException Handling in Action

According to the exception mentioned above, we must catch “NoSuchElementException” and print the proper log messages to guarantee that our test fails with the proper error message.

We use the try and except method to catch the exception when it is raised in the test script. The “try” block lets you check the code for errors, while the “except” block lets you handle the errors or exceptions raised.

Chrome

Firefox

Execution:

Use the terminal to enter the following command to perform Selenium Python testing in parallel on the LambdaTest Grid.

The tests will be executed successfully.

The passed tests will be shown as follows in the LambdaTest Dashboard.

The passed tests will be shown as follows in the LambdaTest Dashboard.

Code Walkthrough:

The “try” block will run the find_element() argument and take in the By query to locate an element using its name in the URL provided.

Step 1: In the browser’s inspect tool, click on Console and type the following command to find the element with the name “p-10”.

The test does not fail since the element with the name “p-10” does not exist. The “except” block will run, catching the exception.

Step 2: The try and except code block is the same in Chrome and Firefox text scripts.

Chrome

Firefox

StaleElementReferenceException

This exception is raised whenever an element is not present in the DOM or is deleted.

Scenario 1 (Chrome Browser)

1. Go to the URL link https://ecommerce-playground.lambdatest.io/index.php?route=account/login.
2. Find the reference to the email and password text fields.
3. Click on a link that reloads the entire web page.
4. Enter the password into the password field with the reference we located before the web page reloaded.

Scenario 2 (Firefox Browser)

1. Go to the URL link https://ecommerce-playground.lambdatest.io/index.php?route=account/login.
2. Find the reference to the email and password text fields.
3. Click on a link that reloads the entire web page.
4. Enter the password into the password field with the reference we located before the web page reloaded.

Implementation (Scenario 1 on the Chrome Browser):

FileName – test_staleelement_chrome.py

Implementation (Scenario 2 on the Firefox Browser):

FileName – test_staleelement_firefox.py

How To Handle Errors And Exceptions In Selenium Python

Eugene Kwaka

Posted On: July 20, 2022

564160 Views

18 Min Read

• Home
• >
• Blog
• >
• How To Handle Errors And Exceptions In Selenium Python

In the world of automation testing, Selenium is a free and open-source framework used to perform web application testing in web browsers like Chrome, Safari, Firefox, Opera, and Edge. You can write Selenium IDE tests using various programming languages such as Python, Java, JavaScript(Node.js), Kotlin, Ruby, PHP, and C#.

While the advantages of automated testing using Selenium are endless, there are incidences of errors and exceptions that happen regularly in the testing tool (or framework). When a program’s execution is disrupted during run-time, an exception is raised, preventing further instructions from being executed. Runtime errors are raised when you perform an unanticipated operation during runtime.

Exception and error handling is a programming mechanism by which the occurrence of errors and exceptions that halt the execution of a program are responded to by the program to ensure the normal execution of code.

In this blog on handling exceptions in Selenium Python, we will look at the variety of exceptions and errors that can happen when a Selenium test is running. By the end of this blog, you will be able to implement error and exception handling for Selenium automation tests.

So, let’s get started!

TABLE OF CONTENTS

Introduction to Errors and Exceptions in Selenium Python

For a program or application to run, a developer must write code that tests every aspect of its functionality. However, the instructions outlined in the code sometimes do not execute as intended.

For QA engineers, the same rule holds when writing code used to test the features and functionality of the applications that have been created to ensure that the application is ready for production and then shipped to the users.

Here is an analogy to help you better understand errors and exceptions in Selenium Python.

Imagine you have a work meeting on Zoom or any online video conference application while at home. During the meeting, the electricity was cut off, which is reported to have affected the whole city. You have no choice but to call off the meeting and wait for the electricity to be reinstated. Akin to this, errors are raised during runtime, and rectifying them is nearly impossible.

In contrast, exceptions are events that raise interruptions while an application runs and can be rectified using exception handling.

Exceptions in Selenium Python are generally classified into two types.

• Checked Exceptions
• Unchecked Exceptions

Checked Exception handling in Selenium is conducted while writing the code. On the other hand, Unchecked Exceptions are raised during runtime and can generate fatal errors compared to the former type of exception.

The class hierarchy of error and exceptions in Selenium Python

You can quickly sharpen your knowledge of exceptions in Selenium Python by reading through this detailed blog on different exceptions in Selenium.

Performing Selenium automated browser testing differs across the ecosystem in which the tests are being carried out. The test scripts may differ depending on the operating systems, browsers, or programming languages they are written in. Therefore, the raised errors andexceptions in Selenium Python may be different. For example, if the browsers don’t have the specified element, Selenium testing of an element property in web browsers may raise exceptions like NoSuchElementException.

To ensure that the applications function correctly and obstruct users’ interactions with the finished product, it is advised that Selenium error and exception handling be used as a standard practice.

Common Exceptions in Selenium Python

According to a recent Stack Overflow developer survey, Python is the fourth most popular programming language among developers.

It offers a robust support system for test automation frameworks and is the most user-friendly and straightforward programming language available.

Errors and exceptions in Selenium Python are common and can occur when writing tests. The exception instances must be derived from a class that inherits from BaseException. If two exception instances do not have a subclass relationship, they are not considered equal despite having the same properties, such as names.

While writing code for the test scripts, the code can run into built-in exceptions, or you can raise exceptions in the code. The interpreter or built-in functions generate the built-in exceptions.

The selenium.common.exceptions package contains the exception classes, which can be imported in the following way.

Syntax: from selenium.common.exceptions import [Exception Name]

An example of an exception being imported is below:

This exception indicates that the website does not contain the attribute of the element being looked for.

Other exceptions in Selenium Python include:

• TimeOutException

When a command does not complete in the time duration set (seconds), this exception is raised or thrown. The wait time can either be implicitly or explicitly defined.

• NoSuchElementException

When an element cannot be found, this exception is raised or thrown. Nonetheless, different factors can lead to this exception being generated:

• The element is not yet in the DOM when the find operation is performed because the page loading is in progress.
• Incorrect element locator is used in the source code.

• ElementNotInteractableException

Such exceptions in Selenium Python is raised whenever an element in the DOM is present but cannot be interacted with.

• ElementNotVisibleException

This exception typically arises when the interaction involves clicking or reading text from an element that is not visible in the DOM.

• StaleElementReferenceException

An outdated or unavailable element in the DOM is referred to as a stale element. A reference to an element that is currently “stale” will raise or throw this exception.

For example, the following reasons could lead to the StaleElementReferenceException exception:

• After the element was located, the page either changed or was refreshed.
• A refreshed context may have contained the element.
• Complete deletion of the referenced web element.

• ElementClickInterceptedException

This exception arises when the element receiving the interaction impedes the element intended to be clicked, thereby preventing the Element Click operation from being performed.

• NoSuchCookieException

This exception will be raised if a cookie with the specified path name is not contained amongst the corresponding cookies of an active document in the current browsing session. To learn more about cookies in Selenium, check out this detailed tutorial on handling cookies in the Selenium WebDriver.

Watch this video to understand how you can handle Cookies and perform different operations like deleting, getting the parameter values, and adding them to Selenium WebDriver using Java.

A command with improper or incorrect argument inputs will raise an InvalidArgumentException.

• InvalidElementStateException

This exception is raised when we try to perform an operation that does not apply to an element. For example, if we perform a click operation on a radio button that is disabled, the exception will be raised, and hence the command given cannot be executed.

• NoSuchWindowException

This exception is thrown when the intended window target cannot be found.

If you are a Python programmer looking to make a mark, you can take your career to the next level with the Selenium Python 101 certification from LambdaTest.

Here’s a short glimpse of the Selenium Python 101 certification from LambdaTest:

Handling Errors and Exceptions in Selenium Python

Handling errors and exceptions in Selenium Python are vital when writing production-ready code, since exceptions and errors can arise for different reasons, as discussed earlier.

A prerequisite to writing tests using Selenium Python is to install Python and Selenium on your machine. When using Python for Selenium testing, the default framework used is PyUnit, also known as unittest, which is influenced by JUnit. It functions similarly to other unit testing frameworks.

However, in this blog on handling errors and exceptions in Selenium Python, we will use Pytest, another Python testing framework that supports functions, APIs, and unit testing. It is compatible with the current versions of Python and is easy to configure using the Python Package Manager (pip) command in the terminal.

If you are new to testing using Selenium Python, here is a detailed step-by-step tutorial on how to get started with Selenium Python. You will learn how to configure Python, Selenium, and Pytest on your machine to start automation testing with Selenium. You can learn more about Pytest through this Selenium Pytest tutorial.

Project Setup

For the test project setup, we are using the Visual Studio (VS) Code IDE to write the test scripts. Alternatively, there are other IDEs available, such as Pycharm, Atom, and Sublime Text, that you can use as well.

For the package manager, we will use Poetry, a Python tool that manages and packages the necessary dependencies in a specific virtual environment for your project. You can declare the libraries your project depends on, and it will take care of managing (installing and updating) them.

To install Poetry on your local machine’s terminal, please use the following command:
For Windows

pip install poetry

For Mac

pip3 install poetry (depends on the Python version you are using).

Move to the directory where your project will be contained.

To initialize Poetry in the terminal, we use the command poetry init. This command will generate a pyproject.toml configuration file containing the build system requirements for Python projects.

14 Oct 2018

Selenium is a very versatile web scraping tool that is accessible via multiple programming languages.

It’s distinguished from text-parsing scrapers like BeautifulSoup as it actually simulates a web navigation experience, enabling you to scrape website running on a lot of Javascript and iframes.

That makes Selenium especially powerful when you are in need of scraping large websites, like e-commerce sites.

However, as with large websites, the pages you scrape won’t be totally identical with one another.

Hence, error or exception handling is very, very important.

Without proper exception handling, you may face errors after errors and waste time, as any error will simply halt your scraping work.

This is especially bad when you have set up your scraping task to take place over lunch or overnight.

Missing Element

Sometimes, certain pages do not have a certain element, which is very common.

For example, you might be scraping Amazon for products’ reviews. Some products that do not have any reviews simply do not have any review element to show you.

This can be easily solved by appending a «» or None to the list that you’re populating your scrape result.

from selenium.common.exceptions import NoSuchElementException

reviews = []

for page in pages_to_scrape:
  try:
    # Insert your scraping action here
    reviews.append(driver.find_element_by_css_selector('div.review').text)
  except NoSuchElementException:
    # Just append a None or ""
    reviews.append(None)
    

Timeout Exception

Some websites are simply slow or too small that your scraping has caused their server to overload.

The latter is always bad and you shouldn’t crash other people’s websites when scraping.

In any case, timeouts (i.e. page failed to load) are common on large websites.

However, I won’t recommend catching this error unless you know from experience that the website is prone to timeouts. It can be a huge waste of resource if the website has a 0.01% chance of timeout.

from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.common.exceptions import TimeoutException

driver.get("your url")
# Remove the while loop and break if you don't want to try again when it took too long
while True:
  try:
    # Define an element that you can start scraping when it appears
    # If the element appears after 5 seconds, break the loop and continue
    WebDriverWait(driver, 5).until(EC.presence_of_element_located((By.CSS_SELECTOR, "your selector")))
    break
  except TimeoutException:
    # If the loading took too long, print message and try again
    print("Loading took too much time!")

Element Click Intercepted Exception

This error happens when the element you try to click (e.g. the «next page» button) gets blocked by another element and becomes unclickable.

The common cause of this is a pop-up being triggered, or there is a chat box that appears at the bottom-right of the page.

There are a few ways to solve this. The first way is to close the pop-up.

from selenium.common.exceptions import ElementClickInterceptedException

try:
  # Tries to click an element
  driver.find_element_by_css_selector("button selector").click()
except ElementClickInterceptedException:
  # If pop-up overlay appears, click the X button to close
  time.sleep(2) # Sometimes the pop-up takes time to load
  driver.find_element_by_css_selector("close button selector").click()

You may also use Javascript to hide that element (credit to Louis’ StackOverflow answer):

from selenium.common.exceptions import ElementClickInterceptedException

try:
  # Tries to click an element
  driver.find_element_by_css_selector("button selector").click()
except ElementClickInterceptedException:
  element = driver.find_element_by_class_name("blocking element's class")
  driver.execute_script("""
            var element = arguments[0];
            element.parentNode.removeChild(element);
            """, element)

If it’s not a pop-up, the problem could be solved by scrolling away, hoping that the blocking element moves with you and away from the button/link to be clicked.

from selenium.common.exceptions import ElementClickInterceptedException

try:
  # Tries to click an element
  driver.find_element_by_css_selector("button selector").click()
except ElementClickInterceptedException:
  # Use Javascript to scroll down to bottom of page
  driver.execute_script("window.scrollTo(0, document.body.scrollHeight);")

Stale Element

Stale element happens when the element is was deleted or no longer attached to the DOM. 

Though a not very common error, some websites are prone to having this error.

When encountered with this error, you can just try again for a number of times.

from selenium.common.exceptions import StaleElementReferenceException

while True:    
  try:
    item_list.append(driver.find_element_by_id("item id").text)
  except StaleElementReferenceException:
    continue # If StaleElement appears, try again
  break # once try is successful, stop while loop

Best Practice — Error Handling & Exceptions

Only use necessary error exceptions

Catching errors and using these exceptions slows your code down significantly. It can cause a regular 1-hour scraping task to double in time especially if you wrap all your scraping actions with error exceptions.

Sometimes it’s totally inescapable, and that’s when a full coverage of error exceptions is necessary so that you can run it overnight without any worries.

However, I recommend to do a trial and error on your code and implement error exceptions only when you encounter them.

Start with a small, representative sample of your web pages to find out the type of errors that can happen.

Use placeholder element before appending to a list

If you’re scraping a few elements in a row, it’s best to assign the result of the scrape to a temporary, placeholder variable before appending to a list.

This is because if you’re appending all to their respective lists, an error in the later stages will cause your prior appended lists having more elements.

# ====================
# Use this way
# ====================
try:
  item_one_temp = driver.find_element_by_id("item one id").text
  item_two_temp = driver.find_element_by_id("item two id").text
  item_one.append(item_one_temp)
  item_two.append(item_two_temp)
except NoSuchElementException:
  item_one.append(None)
  item_two.append(None)

# ====================
# Instead of this
# ====================
try:
  item_one.append(driver.find_element_by_id("item one id").text)
  # if the next element does not exist, item_one list is already appended
  # i.e. one of your list is longer than another
  item_two.append(driver.find_element_by_id("item two id").text)
except NoSuchElementException:
  item_one.append(None)
  item_two.append(None)

Specify specific errors, unless your action plan for any error is the same

It’s useful to specify specific errors that you expect as different errors require different treatments.

Only use a broad «except» statements if you’re planning to do the same if any error arises.

I wish that I know all this before I started scraping as I had to waste a lot of time on StackOverflow. Hope this guide has been useful

Самые частые exceptions в Selenium и способы устранения

• StaleElementReferenceException
• NoSuchElementException
• ElementClickInterceptedException

• NoSuchWindowException
• NoSuchFrameException
• NoAlertPresentException
• InvalidSelectorException
• TimeoutException
• ElementNotVisibleException
• ElementNotSelectableException
• NoSuchSessionException

Для начала, в чем разница между error и exception в Selenium?

• Ошибки типа error — более серьезная вещь, возникают в тестовом окружении, и достаточно трудны для исправления (по крайней мере для новичка в QA)
• Ошибки типа exception возникают в тестируемом приложении (AuT), и легко могут быть откорректированы тестировщиком, чему и посвящен данный материал.

3 самых частых exceptions в Selenium

Ошибка StaleElementReferenceException

Возможно, самый распространенный “эксепшен” у тестировщиков в Selenium (по крайней мере, о нем часто спрашивают на собеседованиях). Это сообщение означает, что веб-элемент по какой-то причине уже как бы “откреплен” от текущего DOM — сначала был в DOM, но после изменений в DOM он:

• Был удален (реже)
• “Завис” и теперь недоступен для действий с ним (чаще)

Причины ошибки StaleElementReferenceException

• Веб-элемента нет в текущем состоянии DOM.
• Веб-элемент удален из DOM. 

Почему так случилось? 

• После перезагрузки страницы (Page Refresh)
• Или выхода пользователя из страницы
• Или веб-элемент по какой-то причине заменен на другой, с идентичными атрибутами

Как обработать ошибку StaleElementReferenceException

• Обновить страницу, и теперь проверить веб-элемент. (Не рекомендуется, если при перезагрузке стираются сессионные данные / введенные пользователем данные)

• Для проверки элемента воспользоваться интерфейсом JavaScriptExecutor
• Имплементировать конструкцию try-catch, то есть “ловить” элемент блоком catch
• Применить эксплицитное ожидание (explicit wait) — то есть ожидать появления элемента
• Попытаться применить Dynamic XPath для обработки DOM-операций
• Попытаться работать через Page Factory Model

Ошибка NoSuchElementException

WebDriver не может найти локальный элемент, то есть через метод FindBy кажется нельзя найти этот элемент.

Причины ошибки NoSuchElementException

• Банальная причина: неправильно прописан локатор в методе findElement(by)
• Имя элемента изменено разработчиком
• Позиция элемента изменилась (если ищут локатором XPath)
• Время загрузки элемента прописано слишком большое

Как устранить причину NoSuchElementException

• “Пофиксить” некорректный локатор
• Или добавить wait-команду
• Или добавить блок try-catch, и/или эксплицитное ожидание элемента

Ошибка ElementClickInterceptedException

Невозможно выполнить команду, из-за того что элемент, “получающий” событие, скрывает за собой запрашиваемый элемент.

Причины ошибки ElementClickInterceptedException

• Элементы “перекрываются” между собой
• Один из элементов не загрузился как положено
• Один из элементов отключен (disabled)
• Элемент не в фокусе
• Действие с некорректным веб-элементом
• Этот элемент нельзя искать на странице по его координатам

Как устранить ElementClickInterceptedException

• Добавить wait-ожидание пока элемент не будет доступен
• Применить JavascriptExecutor для операции клика
• Если элемент “некликабельный”, найти и закрыть “накрывающий” элемент (находящийся сверху нужного нам)
• Если элементу нужен фокус, перейти на активный элемент и выполнить клик, используя класс Action.
• Если для идентификации элемента используются координаты, попробовать сначала развернуть окно в полностью развернутое состояние.

Выше речь шла о самых распространенных “эксепшенах”, возникающих у тестировщиков в Selenium. Далее - о менее распространенных, поэтому о них чуть менее подробно.

NoSuchWindowException

Достаточно частая ошибка в Selenium WebDriver, когда текущий список окон некорректно обновился — предыдущего окна не существует, значит нельзя переключиться на него.

Решение: через метод WebDriver’а, driver.getWindowHandles().

NoSuchFrameException

Возникает аналогично предыдущему (NoSuchWindowException) — при переключении между фреймами один из них становится недоступен.

Решение: как в предыдущем примере.

NoAlertPresentException

Пользователь пытается перейти к еще несуществующему “алерту”. Такое бывает, когда тест “слишком быстрый”. Тест пытается найти “алерт”, который еще не открыт браузером.

Решение: чтобы избежать этой ошибки, или предотвратить ее, применяется эксплицитное или быстрое ожидание (explicit wait, fluent wait), желательно во всех случаях с alert’ами.

InvalidSelectorException

Некорректный селектор. В 99% случаев неправильно написано имя.

Решение: внимательность.

TimeoutException

Операция не выполнилась (не завершилась) в нужное время. 

Ожидания (waits) грамотно применяются опытными тестировщиками во избежание частой ошибки №2, NoSuchElementException, однако если элементы страницы не загрузились в прописанное wait-время, будет “выброшена” ошибка timeoutException.

Решение: тривиальное — узнать (оценить) среднее время загрузки страницы и “подобрать” к нему подходящее wait-время.

ElementNotVisibleException

WebDriver пытается найти элемент, по какой-то причине “заслоненный” другим, или в состоянии “невидимый”. 

Решение: узнать причину “невидимости” — это или проблема с вложенными элементами (и тогда найти и исправить проблемный элемент), или с “перекрытием элементов по времени” (и значит применить эксплицитное wait-ожидание).

ElementNotSelectableException

Этот exception относится к тому же типу, что InvalidElementStateException — элемент хотя и есть на странице, но выбран (отмечен, кликнут) быть не может.

Решение: грамотное применение wait-ожидания.

NoSuchSessionException

Такая ошибка “выбрасывается”, когда метод вызван уже после закрытия браузера — после того как браузер закрылся “самопроизвольно” в результате неожиданного сбоя.

Решение: браузер должен регулярно обновляться, и быть в стабильной версии.

An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program’s instructions.

ElementClickInterceptedException :

ElementNotInteractableException :

<input type='button' height=0px width=0px value='save'>

// click the button which has width=0 and height=0
driver.find_element_by_xpath("//input[@type='button']")).click();

ElementNotSelectableException :

ElementNotSelectableException is related with Select in selenium when the user tries o select an option that is not selectable.

ElementNotVisibleException :

1. Clicking an element that is not visible
2. sendkeys to element which is not visible
3. The element may not be visible because there are more elements under different pages, but that page source code is still present in the cache.

Code which causes the ElementNotVisibleException :

<input type='button' hidden=true value='save'>

// click the button which is hidden (not visible)
driver.find_element_by_xpath("//input[@type='button']")).click();

ErrorInResponseException :

Thrown when an error has occurred on the server-side. This may happen when communicating with the firefox extension or the remote driver server.

InvalidArgumentException :

The arguments passed to a command are either invalid or malformed.

InvalidCoordinatesException :

• When we run our test in different sizes of monitors, we may face this issue.

InvalidElementStateException :

• When element state is disabled

Code which causes the InvalidElementStateException :

<input type='button' disabled=true value='save'>

// click the button which is disabled
driver.find_element_by_xpath("//input[@type='button']")).click();

InvalidSelectorException :

Thrown when the selector which is used to find an element does not return a WebElement. Currently, this only happens when the selector is an XPath expression, and it is either syntactically invalid (i.e., it is not an XPath expression), or the expression does not select WebElements (e.g. «count(//input»).

InvalidSwitchToTargetException :

Thrown, when frame or window target to be switched, doesn’t exist.

MoveTargetOutOfBoundsException :

• Change of screen size ( test cases are written in desktop, but current execution is happening laptop, considering that desktop screen size is bigger)

Code which causes the MoveTargetOutOfBoundsException :

actions = new Actions(driver);
actions.mouseMove( 10, 25 )
actions.perform();

NoAlertPresentException :

• NoAlertPresentException occurs because of one of the below reasons
• When a user tries to access an alert that is not present in at the current time.
• When javascript is blocked in the browser
• Not giving enough time for the alert to load
• When an alert is already closed

Code which causes the NoAlertPresentException :

driver.switch_to_alert()

NoSuchElementException :

• NoSuchElementException occurs because of one of the below reasons
• Either Xpath you specified for the element is wrong.
• The second reason is AJAX has not returned yet, and you’ve already obtained NoSuchElementException.
• The page is still being rendered, but you’ve already finished your element search because of a low wait time.
• The element is not on the page at all

Code which causes the NoSuchElementException :

driver.find_element_by_xpath("//label/span")

# the error message
<div" class="warn">Exception Message:org.openqa.selenium.
NoSuchElementException: Unable to locate element: //label/span

NoSuchFrameException :

• NoSuchFrameException occurs because of one of the below reasons.
• There is no frame with given details, or the details changed during the page loading time.
• Target Frame is not a frame if the locators match exactly with another element( as the first instance).
• We have not given enough wait time to load the frame.

Code which causes the NoSuchFrameException :

driver.switch_to_frame("frame1");

NoSuchWindowException :

• The current window closed.
• The target window is not opened yet, but you were trying to perform the operation.
• When the target window has been closed, but still the code attempted to operate the target window.

Code which causes the NoSuchWindowException :

driver.switch_to_window("window Gu ID")

ScreenshotException :

• When we try to take a screenshot in the headless browser(phantomjs, htmlunitdriver) without enabling the screenshot functionality.

Code which causes the ScreenshotException :

TakesScreenshot screenShot =((TakesScreenshot) driver);

TimeoutException :

• Element is not present or given Condition is not met.
• When the given timeout is very low. When the page takes more time to load. When executeAsyncScript() takes more time to return its operation

Code which causes the TimeoutException :

WebDriverWait wait = new WebDriverWait(driver, 30);
WebElement idElement;
idElement = wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("123")));

UnexpectedAlertPresentException :

Thrown when an unexpected alert has appeared. Usually raised when an expected modal is blocking webdriver form executing any more commands.

UnexpectedTagNameException :

• The dropdown is formed without using the select tag name.
• The HTML code might have changed to a non-select tag after writing the test automation code.
• If dropdown HTML code is specific to the browser used, Sometimes code can be rendered based on the browser.

Code which causes the UnexpectedTagNameException :

// throws the UnexpectedTagNameException
dropdown = Select(driver.find_element_by_id('//input'))

// this will not throw exception
dropdown = Select(driver.find_element_by_id('//select'))

About Author :

I am Pavankumar, Having 8.5 years of experience currently working in Video/Live Analytics project.