使用Selenium爬取页面时遇验证码需终止程序，求实现方法

Great question—when scraping at scale, accidentally dismissing captcha prompts is a surefire way to get your IP or account blocked. Let’s walk through a reliable solution to detect these captcha alerts and terminate your program before that happens.

Step 1: Differentiate Captcha Alerts from Regular Alerts #

Most regular alerts have generic messages (like "Are you sure?" or "Action completed!"), while captcha prompts will include keywords tied to security checks. We can leverage this to build a conditional check before automatically accepting alerts.

Here’s a practical code snippet:

from selenium.common.exceptions import NoAlertPresentException
import sys

def handle_alert(browser):
    try:
        # Switch to the alert if one exists
        alert = browser.switch_to.alert
        alert_text = alert.text.lower()
        
        # Define keywords that signal a captcha prompt (adjust these for your target site)
        captcha_triggers = ["captcha", "security check", "人机验证", "verify you're human"]
        
        if any(trigger in alert_text for trigger in captcha_triggers):
            print("⚠️ Captcha detected! Terminating program to avoid being blocked.")
            # Dismiss the alert (cleaning up before exit is better than leaving it hanging)
            alert.dismiss()
            browser.quit()
            sys.exit(1)
        else:
            # It's a regular alert—safe to accept
            alert.accept()
    except NoAlertPresentException:
        # No alert to handle, proceed with your scraping logic
        pass

# Call this function after navigating to each page
handle_alert(browser)

Step 2: Add Robust Waiting with WebDriverWait #

Instead of immediately checking for alerts (which can miss slow-loading prompts), use WebDriverWait to wait for alerts to appear with a timeout. This makes your code far more reliable:

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

def handle_alert_safely(browser):
    try:
        # Wait up to 5 seconds for an alert to show up
        alert = WebDriverWait(browser, 5).until(EC.alert_is_present())
        alert_text = alert.text.lower()
        
        captcha_triggers = ["captcha", "security check", "人机验证"]
        if any(trigger in alert_text for trigger in captcha_triggers):
            print("⚠️ Captcha encountered! Stopping scraping immediately.")
            alert.dismiss()
            browser.quit()
            sys.exit(1)
        else:
            alert.accept()
    except TimeoutException:
        # No alert appeared in time—continue scraping
        pass

Step 3: Check for Non-Alert Captcha Elements #

Some sites don’t use alerts for captchas—they show inline modals or form elements. Add a check for these cases too:

from selenium.common.exceptions import NoSuchElementException

def check_for_captcha(browser):
    try:
        # Adjust the selector to match your target site's captcha container (use ID, class, or XPath)
        captcha_box = browser.find_element(By.CLASS_NAME, "captcha-modal")
        if captcha_box.is_displayed():
            print("⚠️ Captcha found on page! Terminating program.")
            browser.quit()
            sys.exit(1)
    except NoSuchElementException:
        # No captcha element found—keep going
        pass

# Call this after page loads, alongside the alert handler
check_for_captcha(browser)

Bonus Tips to Reduce Captcha Triggers #

• Add random delays between requests (e.g., time.sleep(random.uniform(1, 3))) to mimic human browsing speed.
• Rotate user agents and proxies if you’re scraping very large volumes of pages.
• Avoid rapid-fire clicks or form submissions—pace your actions like a real user would.

内容的提问来源于stack exchange，提问作者Luiza Rodrigues