Selenium with Python Essentials Cheatsheet

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Testing & Debugging / Selenium

June 18, 2025 00:31

automation

python

selenium

web testing

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Core Actions & Setup

SETUP & IMPORTS

1. Install Selenium:

pip install selenium
pip install webdriver_manager

2. Basic Imports:

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.support.ui import Select

3. Launching Browsers (Chrome Example):

from selenium.webdriver.chrome.service import Service
from webdriver_manager.chrome import ChromeDriverManager

# For Chrome
service = Service(ChromeDriverManager().install())
driver = webdriver.Chrome(service=service)

# For Firefox
# from selenium.webdriver.firefox.service import Service as FirefoxService
# from webdriver_manager.firefox import GeckoDriverManager
# service = FirefoxService(GeckoDriverManager().install())
# driver = webdriver.Firefox(service=service)

4. Headless Mode (Chrome):

from selenium.webdriver.chrome.options import Options
chrome_options = Options()
chrome_options.add_argument("--headless")
driver = webdriver.Chrome(service=service, options=chrome_options)

Pro Tip: Use webdriver_manager to automatically handle WebDriver binaries, saving you from manual downloads and path configurations.

LOCATING ELEMENTS

find_element() vs find_elements()

find_element(): Returns the first matching element or raises NoSuchElementException.
find_elements(): Returns a list of all matching elements (empty list if none found).

By.ID

driver.find_element(By.ID, "username")

By.NAME

driver.find_element(By.NAME, "password")

By.CLASS_NAME

driver.find_element(By.CLASS_NAME, "submit-button")

By.TAG_NAME

driver.find_element(By.TAG_NAME, "a") # First link
driver.find_elements(By.TAG_NAME, "div") # All div elements

By.LINK_TEXT / By.PARTIAL_LINK_TEXT

driver.find_element(By.LINK_TEXT, "Click Me")
driver.find_element(By.PARTIAL_LINK_TEXT, "Click")

By.XPATH

driver.find_element(By.XPATH, "//input[@type='text']")
driver.find_element(By.XPATH, "//div[contains(text(), 'Hello')]")

By.CSS_SELECTOR

driver.find_element(By.CSS_SELECTOR, "#loginForm input[type='submit']")
driver.find_element(By.CSS_SELECTOR, ".menu-item:nth-child(2)")

Pro Tip: Prioritize By.ID as it’s the most robust and fastest. If not available, By.CSS_SELECTOR is generally preferred over By.XPATH for performance and readability, though XPATH is more powerful for complex queries.

INTERACTING WITH ELEMENTS

Clicking an element

button = driver.find_element(By.ID, "submitBtn")
button.click()

Typing into a text field

username_field = driver.find_element(By.NAME, "username")
username_field.send_keys("testuser")

Clearing text

text_area = driver.find_element(By.TAG_NAME, "textarea")
text_area.clear()

Sending special keys

input_field.send_keys(Keys.RETURN) # Press Enter
input_field.send_keys(Keys.CONTROL + 'a') # Select all

Dropdowns (Select class)

from selenium.webdriver.support.ui import Select

dropdown = Select(driver.find_element(By.ID, "myDropdown"))
dropdown.select_by_visible_text("Option Two")
dropdown.select_by_value("value3")
dropdown.select_by_index(0) # First option

# Get all options
options = dropdown.options

Checkboxes & Radio Buttons

checkbox = driver.find_element(By.ID, "agreeCheckbox")
if not checkbox.is_selected():
    checkbox.click()

radio_button = driver.find_element(By.ID, "optionRadio")
radio_button.click()

Getting element text / attribute

element = driver.find_element(By.ID, "statusMessage")
print(element.text) # Get visible text
print(element.get_attribute("value")) # Get input value
print(element.get_attribute("href")) # Get link URL

Common Pitfall: ElementNotInteractableException often means the element is not yet visible or clickable. Use explicit waits before attempting interaction.

Advanced Techniques & Control

WAITING STRATEGIES

time.sleep()

import time
time.sleep(5) # Waits for 5 seconds (NOT RECOMMENDED for robustness)

Note: This is a fixed delay and should be avoided in most cases as it makes tests slow and brittle.

Implicit Wait

driver.implicitly_wait(10) # Waits up to 10 seconds for elements to appear.

Explanation: Applied globally for the WebDriver instance. Selenium will poll the DOM for a certain amount of time when trying to find an element.

Explicit Wait (WebDriverWait)

from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

wait = WebDriverWait(driver, 10) # Wait up to 10 seconds

# Wait for element to be clickable
login_button = wait.until(EC.element_to_be_clickable((By.ID, "loginBtn")))
login_button.click()

Explanation: Waits for a specific condition to be met before proceeding. More flexible and robust than implicit waits.

Common expected_conditions (EC)

EC.presence_of_element_located(locator)
EC.visibility_of_element_located(locator)
EC.element_to_be_clickable(locator)
EC.text_to_be_present_in_element(locator, text)
EC.title_contains(title)
EC.alert_is_present()

Custom Wait Conditions

# Wait until an element's attribute has a specific value
wait.until(lambda d: d.find_element(By.ID, "status").get_attribute("data-state") == "ready")

Pro Tip: Use explicit waits for specific conditions, especially before interacting with dynamic elements. Use implicit waits as a fallback for general element presence, but be cautious as they can sometimes conflict with explicit waits causing unexpected delays.

NAVIGATION & BROWSER CONTROL

Navigate to a URL

driver.get("https://www.example.com")

Browser history

driver.back()     # Go back in browser history
driver.forward()  # Go forward in browser history
driver.refresh()  # Refresh the current page

Window size & position

driver.maximize_window()
driver.minimize_window()
driver.set_window_size(1024, 768) # Width, Height

Close vs Quit

driver.close() # Closes the current window/tab
driver.quit()  # Closes all windows/tabs and quits the browser session

Switching Windows/Tabs

# Open new tab (example)
driver.execute_script("window.open('about:blank','_blank');")

# Get all window handles (unique IDs)
window_handles = driver.window_handles

# Switch to the new tab (usually the last one)
driver.switch_to.window(window_handles[-1])
driver.get("https://www.new-tab.com")

# Switch back to the original tab
driver.switch_to.window(window_handles[0])

Switching Frames

# By ID or Name
driver.switch_to.frame("myiframe")

# By WebElement
iframe_element = driver.find_element(By.TAG_NAME, "iframe")
driver.switch_to.frame(iframe_element)

# Switch back to the main content
driver.switch_to.default_content()

Common Pitfall: Forgetting to call driver.quit() at the end of your test suite. This leaves browser processes running, consuming resources and potentially causing issues in subsequent runs.

SCREENSHOTS & LOGGING

Capture full page screenshot

driver.save_screenshot("full_page.png")

Capture element screenshot

element = driver.find_element(By.ID, "myElement")
element.screenshot("element_screenshot.png")

Basic Python Logging

import logging

logging.basicConfig(level=logging.INFO,
                    format='%(asctime)s - %(levelname)s - %(message)s',
                    filename='test_log.log',
                    filemode='w')

logging.info("Navigating to homepage")
logging.warning("Element not found within 5 seconds")
logging.error("Test failed: Login button not clickable")

Pro Tip: Include timestamps in your screenshot filenames (e.g., screenshot_{time.strftime('%Y%m%d-%H%M%S')}.png) to easily differentiate them when debugging test failures over time.

COMMON ERRORS & DEBUGGING

NoSuchElementException

Cause: Element not found on the page or not present in the DOM when searched.
Solution: Verify locator, ensure element is present/visible (use explicit waits), or switch to correct frame/window.

TimeoutException

Cause: An explicit wait condition was not met within the specified timeout duration.
Solution: Increase wait time, check if the condition is realistic, or investigate why the element isn’t reaching the expected state.

ElementNotInteractableException

Cause: Element is present but not in a state to be interacted with (e.g., hidden, disabled, overlaid).
Solution: Wait for the element to become clickable/visible, use execute_script to interact if truly necessary, or check for pop-ups/modals obstructing it.

StaleElementReferenceException

Cause: The element reference you hold is no longer attached to the DOM (e.g., page refresh, element reloaded).
Solution: Re-locate the element after the DOM change. Often, wrapping the interaction in a try-except block and re-trying the find operation helps.

Using try/except

from selenium.common.exceptions import NoSuchElementException

try:
    element = driver.find_element(By.ID, "nonExistentElement")
    element.click()
except NoSuchElementException:
    print("Element not found, handling gracefully.")
    # Log the error, take screenshot, or continue test differently

Debugging Tips

Print Statements: Simple but effective for tracing execution.
pdb (Python Debugger): Insert import pdb; pdb.set_trace() to pause execution and inspect variables.
Browser Developer Tools: Crucial for inspecting elements, network requests, and console errors.
Screenshots: Capture screenshots on failure to visualize the state of the page.

Pro Tip: Most common Selenium errors stem from timing issues. Master explicit waits and understand the state of your application’s DOM to write robust and reliable automation scripts.