Selenium: UnexpectedAlertPresentException: unexpected alert open

A JavaScript dialog (alert, confirm or prompt) was open when your script sent a command. While a native dialog is showing, the page is blocked and the driver cannot interact with it. Depending on the session's unhandled prompt behavior, the driver dismisses the dialog and reports this exception (the W3C default is dismiss and notify), so the dialog may already be gone by the time you look.

The alert text is included in the message, which usually explains why it appeared: an unsaved-changes warning on navigation, a validation message, an error from the site, or a confirmation step in a delete flow. In Java this exception is UnhandledAlertException.

What is not wrong: the element or command that failed. It never ran because the dialog was blocking the page.

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

driver.find_element(By.ID, "delete").click()
alert = WebDriverWait(driver, 5).until(EC.alert_is_present())
print(alert.text)
alert.accept()

Map which actions in the application raise native dialogs and handle each one where it occurs. Configure an unhandled prompt behavior for the whole session as a safety net, and log alert text whenever it is triggered so unexpected site errors are not silently dismissed.