Lecture 16

Web-scrapping with Python selenium

Byeong-Hak Choe

bchoe@geneseo.edu

SUNY Geneseo

March 14, 2025

Web-scrapping with Python `selenium`

WebDriver

WebDriver is an wire protocol that defines a language-neutral interface for controlling the behavior of web browsers.
The purpose of WebDriver is to control the behavior of web browsers programmatically, allowing automated interactions such as:
- Extracting webpage content
- Opening a webpage
- Clicking buttons
- Filling out forms
- Running automated tests on web applications
Selenium WebDriver refers to both the language bindings and the implementations of browser-controlling code.

Driver

Each browser requires a specific WebDriver implementation, called a driver.
- Web browsers (e.g., Chrome, Firefox, Edge) do not natively understand Selenium WebDriver commands.
- To bridge this gap, each browser has its own WebDriver implementation, known as a driver.
The driver handles communication between Selenium WebDriver and the browser.
- This driver acts as a middleman between Selenium WebDriver and the actual browser.
Different browsers have specific drivers:
- ChromeDriver for Chrome
- GeckoDriver for Firefox

Interaction Diagram

A simplified diagram of how WebDriver interacts with browser might look like this:

WebDriver interacts with the browser via the driver in a two-way communication process:
1. Sends commands (e.g., open a page, click a button) to the browser.
2. Receives responses from the browser.

Setting up

Install the Chrome or FireFox web-browser if you do not have either of them.
- I will use the Chrome.
Install Selenium using pip:
- On the Spyder Console, run the following:
- pip install selenium
Selenium with Python is a well-documented reference.

Setting up - `webdriver.Chrome()`

To begin with, we import (1) webdriver from selenium and (2) the By and Options classes.
- webdriver.Chrome() opens the Chrome browser that is being controlled by automated test software, selenium.

# Import the necessary modules from the Selenium package
from selenium import webdriver  # Main module to control the browser
from selenium.webdriver.common.by import By  # Helps locate elements on the webpage
from selenium.webdriver.chrome.options import Options  # Allows setting browser options

# Create an instance of Chrome options
options = Options()
options.add_argument("window-size=1400,1200")  # Set the browser window size to 1400x1200

# Initialize the Chrome WebDriver with the specified options
driver = webdriver.Chrome(options=options)  # Correct implementation

# Now you can use 'driver' to control the Chrome browser

`get()` Method in WebDriver

get(url) from webdriver opens the specified URL in a web browser.
When using webdriver in Google Chrome, you may see the message:
- “Chrome is being controlled by automated test software.”

form_url = "https://qavbox.github.io/demo/webtable/"
driver.[?](form_url)
driver.close()
driver.quit()

close() terminates the current browser window.
quit() completely exits the webdriver session, closing a browser window.

Inspecting Web Elements with `find_element()`

Once the Google Chrome window loads with the provided URL, we need to find specific elements to interact with.
- The easiest way to identify elements is by using Developer Tools to inspect the webpage structure.
To inspect an element:
1. Right-click anywhere on the webpage.
2. Select the Inspect option from the pop-up menu.
3. In the Elements panel, hover over the DOM structure to locate the desired element.

Inspecting Web Elements with `find_element()`

When inspecting an element, look for:
- HTML tag (e.g., <input>, <button>, <div>) used for the element.
- Attributes (e.g., id, class, name) that define the element.
- Attribute values that help uniquely identify the element.
- Page structure to understand how elements are nested within each other.

Locating Web Elements by `find_element()` & `find_elements()`

Locating Web Elements by `find_element()`

There are various strategies to locate elements in a page.

find_element(By.ID, "id")
find_element(By.CLASS_NAME, "class name")
find_element(By.NAME, "name")
find_element(By.CSS_SELECTOR, "css selector")
find_element(By.TAG_NAME, "tag name")
find_element(By.LINK_TEXT, "link text")
find_element(By.PARTIAL_LINK_TEXT, "partial link text")
find_element(By.XPATH, "xpath")

Selenium provides the find_element() method to locate elements in a page.
To find multiple elements (these methods will return a list):
- find_elements()

`find_element(By.ID, "")`

find_element(By.ID, "") & find_elements(By.ID, ""):
- Return element(s) that match a given ID attribute value.
Example HTML code where an element has an ID attribute form1:

<form id="form1">...</form>

Example of locating the form using find_element(By.ID, ""):

form = driver.find_element(By.ID, "form1")
form.text  # Retrieves text content if available

`find_element(By.CLASS_NAME, "")`

find_element(By.CLASS_NAME, "") & find_elements(By.CLASS_NAME, ""):
- Return element(s) matching a specific class attribute.
Example HTML code with a homebtn class:

<div class="homebtn" align="center">...</div>

home_button = driver.find_element(By.CLASS_NAME, "homebtn")
home_button.click()  # Clicks the home button
driver.back()  # Navigates back to the previous page

`find_element(By.NAME, "")`

find_element(By.NAME, "") & find_elements(By.NAME, ""):
- Return element(s) with a matching name attribute.
Example HTML code with a name attribute home:

<input type="button" class="btn" name="home" value="Home" />

home_button2 = driver.find_element(By.NAME, "home")
home_button2.click()
driver.back()

`find_element(By.CSS_SELECTOR, "")`

find_element(By.CSS_SELECTOR, "") & find_elements(By.CSS_SELECTOR, ""):
- Locate element(s) using a CSS selector.
Inspect the webpage using browser Developer Tools.
Locate the desired element in the Elements panel.
Right-click and select Copy selector
- Let’s find out CSS selector for the Home button.

home_button3 = driver.find_element(By.CSS_SELECTOR, "body > div > a > input")
home_button3.click()
driver.back()

`find_element(By.TAG_NAME, "")`

find_element(By.TAG_NAME, "") & find_elements(By.TAG_NAME, ""):
- Locate element(s) by a specific HTML tag.

table01 = driver.find_element(By.ID, "table01")
thead = table01.find_element(By.TAG_NAME, "thead")
thead.text

`find_element(By.LINK_TEXT, "")`

find_element(By.LINK_TEXT, "") & find_elements(By.LINK_TEXT, ""):
- Locate link(s) using the exact text displayed.
Example HTML for a Selenium link:

<a href="http://www.selenium.dev/">Selenium</a>

selenium_link = driver.find_element(By.LINK_TEXT, "Selenium")
selenium_link.click()
driver.back()

`find_element(By.PARTIAL_LINK_TEXT, "")`

Finds link(s) containing partial text.

Selen_links = driver.find_elements(By.PARTIAL_LINK_TEXT, "qav")
print(len(Selen_links))
Selen_links[0].click()
driver.back()

`find_element(By.XPATH, "")`

Understanding XPath

find_element(By.XPATH, "") & find_elements(By.XPATH, ""):
- Return element(s) that match the specified XPath query.
XPath is a query language for searching and locating nodes in an XML document.
- Supported by all major web browsers.
- Used in Selenium to find elements when ID, name, or class attributes are not available.
- Powerful for navigating complex HTML structures.

Basic XPath Syntax

//tag_name[@attribute='value']

// → Selects elements anywhere in the document.
tag_name → HTML tag (input, div, span, etc.).
@attribute → Attribute name (id, class, aria-label, etc.).
value → Attribute’s assigned value.

Absolute vs. Relative XPath

Absolute XPath → Defines the full path from the root node.
- Reliable if the webpage structure does not change.
Relative XPath → Defines the path starting from a known element.
- More flexible—doesn’t break as easily if the structure changes.

Example: Finding a Table Element with XPath

XPath can use attributes other than ID, name, or class to locate elements.
Suppose we want to retrieve data from a second table on a webpage.
The table contains multiple <tr> (rows) and <th> (headers) without an easily identifiable ID or class.
find_element(By.TAG_NAME, "") is not reliable due to multiple <tr> and <th> tags.

Extracting XPath from Developer Tools

Inspect the webpage using browser Developer Tools.
Locate the desired element in the Elements panel.
Right-click and select Copy XPath.
Example extracted XPath:

//*[@id="table02"]/tbody/tr[1]/td[1]
/html/body/form/fieldset/div/div/table/tbody/tr[1]/td[1]

Finding an Element Using XPath

Locate “Tiger Nixon” in the second table:

elt = driver.find_element(By.XPATH, '//*[@id="table02"]/tbody/tr[1]/td[1]')
print(elt.text)  # Output the extracted text

When to Use XPath

Use XPath when:
- The element lacks a unique ID or class.
- Other locator methods (By.ID, By.CLASS_NAME, etc.) don’t work.
Limitations:
- XPath is less efficient than ID-based locators.
- Page structure changes may break XPath-based automation.
For our tasks, however, XPath remains a reliable and effective method!

Retrieving Attribute Values with `get_attribute()`

get_attribute() extracts an element’s attribute value.
Useful for retrieving hidden properties not visible on the page.

<a href="https://www.selenium.dev/">Selenium</a>
<input id="btn" class="btn" type="button" onclick="change_text(this)" value="Delete">

driver.find_element(By.XPATH, '//*[@id="table01"]/tbody/tr[2]/td[3]/a').get_attribute('href')
driver.find_element(By.XPATH, '//*[@id="btn"]').get_attribute('value')

Web-scrapping with Python `selenium`

Let’s do Classwork 9!

`NoSuchElementException` and `WebDriverWait`

`NoSuchElementException` and `try-except` blocks

from selenium.common.exceptions import NoSuchElementException
try:
    elem = driver.find_element(By.XPATH, "element_xpath")
    elem.click()
except NoSuchElementException:
    pass

When a web element is not found, it throws the NoSuchElementException.
- try-except can be used to avoid the termination of the selenium code.
This solution is to address the inconsistency in the DOM among the seemingly same pages.

Explicit wait with `time.sleep()`

import time

# example webpage
url = "https://qavbox.github.io/demo/delay/"
driver.get(url)

driver.find_element(By.XPATH, '//*[@id="one"]/input').click()
time.sleep(5)
element = driver.find_element(By.XPATH, '//*[@id="two"]')
element.text

The time.sleep() method is an explicit wait to set the condition to be an exact time period to wait.
In general, a more efficient solution than time.sleep() would be to make WebDriver() wait only as long as required.

Implicit wait with `implicitly_wait()`

driver.find_element(By.XPATH, '//*[@id="oneMore"]/input[1]').click()
driver.implicitly_wait(10)  # Wait up to 10 seconds for elements to appear
element2 = driver.find_element(By.ID, 'delay')
element2.text

Implicit wait with implicitly_wait() directs the webdriver to wait for a certain measure of time before throwing an exception.
- Applies globally for the lifetime of the driver session.
Once this time is set, webdriver will wait for the element before the exception occurs.

Explicit wait with `WebDriverWait` and `EC`

An explicit wait allows you to wait for a specific condition before continuing.
Uses:
- Wait for elements to appear, be visible, or be clickable.
- More flexible and precise than implicit waits.

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

To wait for presence_of_element_located:

element = ( 
  WebDriverWait(driver, 20)  # 20 is timeout in seconds when an expectation is called
  .until(
    EC.presence_of_element_located(
      (By.XPATH, "element_xpath")
      )
    )
)

To wait for visibility_of_element_located:

element = (
  WebDriverWait(driver, 20)
  .until(
    EC.visibility_of_element_located(
      (By.CSS_SELECTOR, "element_css")
      )
  )
)

To wait for element_to_be_clickable:

element = (
  WebDriverWait(driver, 20)
  .until(
    EC.element_to_be_clickable(
      (By.LINK_TEXT, "element_link_text")
      )
    )
)

Web-scrapping with Python `selenium`

Let’s do Classwork 10!

Lecture 16

Web-scrapping with Python selenium

WebDriver

Driver

Interaction Diagram

Setting up

Setting up - webdriver.Chrome()

get() Method in WebDriver

Inspecting Web Elements with find_element()

Inspecting Web Elements with find_element()

Locating Web Elements by find_element() & find_elements()

Locating Web Elements by find_element()

find_element(By.ID, "")

find_element(By.CLASS_NAME, "")

find_element(By.NAME, "")

find_element(By.CSS_SELECTOR, "")

find_element(By.TAG_NAME, "")

find_element(By.LINK_TEXT, "")

find_element(By.PARTIAL_LINK_TEXT, "")

find_element(By.XPATH, "")

Understanding XPath

Basic XPath Syntax

Absolute vs. Relative XPath

Example: Finding a Table Element with XPath

Extracting XPath from Developer Tools

Finding an Element Using XPath

When to Use XPath

Retrieving Attribute Values with get_attribute()

Web-scrapping with Python selenium

NoSuchElementException and WebDriverWait

NoSuchElementException and try-except blocks

Explicit wait with time.sleep()

Implicit wait with implicitly_wait()

Explicit wait with WebDriverWait and EC

Web-scrapping with Python selenium

Web-scrapping with Python `selenium`

Setting up - `webdriver.Chrome()`

`get()` Method in WebDriver

Inspecting Web Elements with `find_element()`

Inspecting Web Elements with `find_element()`

Locating Web Elements by `find_element()` & `find_elements()`

Locating Web Elements by `find_element()`

`find_element(By.ID, "")`

`find_element(By.CLASS_NAME, "")`

`find_element(By.NAME, "")`

`find_element(By.CSS_SELECTOR, "")`

`find_element(By.TAG_NAME, "")`

`find_element(By.LINK_TEXT, "")`

`find_element(By.PARTIAL_LINK_TEXT, "")`

`find_element(By.XPATH, "")`

Retrieving Attribute Values with `get_attribute()`

Web-scrapping with Python `selenium`

`NoSuchElementException` and `WebDriverWait`

`NoSuchElementException` and `try-except` blocks

Explicit wait with `time.sleep()`

Implicit wait with `implicitly_wait()`

Explicit wait with `WebDriverWait` and `EC`

Web-scrapping with Python `selenium`