5 Best Ways to Get Console Log Output from Chrome with Selenium Python API Bindings

Rate this post
Getting Console Log Output from Chrome with Selenium Python API Bindings

πŸ’‘ Problem Formulation: When automating browser interactions using Selenium with Python, developers might need to access the console log output of Chrome to debug JavaScript code or to understand the browser’s behavior in the context of the tested web application. The desired output is a way to programmatically retrieve console log entries using the Selenium WebDriver Python bindings.

Method 1: Using Desired Capabilities

Launch Selenium WebDriver with customized capabilities to capture browser logs. The DesiredCapabilities feature of Selenium allows you to define browser preferences, including enabling the logging feature for browser console output.

Here’s an example:

from selenium import webdriver
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities

capabilities = DesiredCapabilities.CHROME
capabilities['goog:loggingPrefs'] = {'browser': 'ALL'}
driver = webdriver.Chrome(desired_capabilities=capabilities)

# Your test steps here

logs = driver.get_log('browser')
for entry in logs:
    print(entry)

driver.quit()

Output:

{'level': 'SEVERE', 'message': 'http://example.com - Failed to load resource: the server responded with a status of 404 (Not Found)', 'timestamp': 1618316554116}

This code snippet demonstrates how to modify the desired capabilities of Chrome to capture all levels of log entries. Creating a Chrome WebDriver instance with these capabilities enables access to the browser logs which can then be retrieved and printed after the desired test steps are executed.

Method 2: Using ChromeOptions

ChromeOptions allow more fine-grained control and can coalesce several preferences and options to configure the Chrome WebDriver, including enabling console log retrieval.

Here’s an example:

from selenium import webdriver
from selenium.webdriver.chrome.options import Options

chrome_options = Options()
chrome_options.add_experimental_option('w3c', False)
chrome_options.add_experimental_option('perfLoggingPrefs', {'enableNetwork': False, 'enablePage': False, 'enableTimeline': False})
capabilities = chrome_options.to_capabilities()

driver = webdriver.Chrome(desired_capabilities=capabilities)
driver.get("http://example.com")

# Your test steps here

logs = driver.get_log('browser')
for entry in logs:
    print(entry)

driver.quit()

Output:

{'level': 'SEVERE', 'message': 'http://example.com - Console error message...', 'timestamp': 1618316554116}

This method sets up ChromeOptions by adding specific experimental options to suppress performance logging while enabling access to console logs. The browser logs are then available for retrieval with similar commands as Method 1.

Method 3: Using WebDriver Manager

WebDriver Manager is a library that provides a way to automatically manage drivers for different browsers. In addition to simplifying the driver setup process, it can work seamlessly with Selenium to help capture console logs.

Here’s an example:

from selenium import webdriver
from webdriver_manager.chrome import ChromeDriverManager

driver = webdriver.Chrome(ChromeDriverManager().install())

driver.get("http://example.com")

# to enable console log retrieval
driver.execute_script("window.console.log = function(msg){console.old_log(msg);window.last_msg = msg;}")
driver.execute_script("window.console.old_log = window.console.log;")

# Your test steps here
# Now you can get the last log message with:
log_message = driver.execute_script("return window.last_msg;")
print(log_message)

driver.quit()

Output:

'Last console message displayed here...'

This snippet employs WebDriver Manager to set up the Chrome driver and uses JavaScript injection to override the console.log function so that it also sets the last message to a variable on the window object. This is helpful for capturing and accessing the last message output in the console log.

Method 4: Using BrowserMob Proxy

BrowserMob Proxy is a tool that can capture network traffic and also interact with the browser’s console. It acts as a proxy between Selenium and the browser, enabling more advanced features like console log capturing.

Here’s an example:

# Assume that you have BrowserMob Proxy set up and running.

from selenium import webdriver
from browsermobproxy import Server

server = Server("path_to_browsermob-proxy")
server.start()
proxy = server.create_proxy()

chrome_options = webdriver.ChromeOptions()
chrome_options.add_argument(f"--proxy-server={proxy.proxy}")

driver = webdriver.Chrome(chrome_options=chrome_options)
proxy.new_har("example")
driver.get("http://example.com")

# Your test steps here

# Retrieve console log entries via HAR file
logs = proxy.har['log']['entries']
for entry in logs:
    print(entry['request'], entry['response'])

driver.quit()
server.stop()

Output:

Request information for each entry...
Response details for each entry...

This code shows how to set up BrowserMob Proxy to intercept browser traffic and includes capturing console logs. There’s additional setup involved, but once in place, the proxy generates a HAR (HTTP Archive) file that includes detailed logs of all browser interactions.

Bonus One-Liner Method 5: Simple Log Capturing Command

This method demonstrates a one-liner approach to retrieve console logs directly after a page load, assuming that the appropriate capabilities have been set to log browser interactions.

Here’s an example:

print(driver.get_log('browser'))

Output:

A list of dictionaries each representing a log entry.

A quick and straightforward command once the Chrome WebDriver instance has been set up with the correct capabilities, it retrieves and prints the browser logs up to the point of execution.

Summary/Discussion

  • Method 1: Using Desired Capabilities. Straightforward. Requires initial setup.
  • Method 2: Using ChromeOptions. Offers fine control over the browser instance. Experimental options may change in future Chrome versions.
  • Method 3: Using WebDriver Manager. Simplifies driver setup. JavaScript injection may be complex for advanced logging needs.
  • Method 4: Using BrowserMob Proxy. Enables advanced traffic and log monitoring. Additional setup and resources required.
  • Method 5: Simple Log Capturing Command. Quick and easy. Requires capabilities or options to be set prior.