Selenium: NoSuchWindowException: target window already closed

The driver is pointed at a window or tab that no longer exists, or you tried to switch to a handle that is not valid. WebDriver tracks a current window; when that window closes, the driver does not automatically move to another one. Every following command fails with this exception until you switch to a window that is still open.

The typical sequence: a link opens a new tab, the script switches to it, does its work, calls driver.close(), and then keeps sending commands without switching back. Popups that close themselves, such as OAuth or payment windows, cause the same thing without any close() in your code. A user closing the window manually during a run does it too.

What is not wrong: the session. Other windows are still controllable; only the current target is gone. If the last window closed, the session ends and you see InvalidSessionIdException instead.

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

main = driver.current_window_handle
driver.find_element("link text", "Open report").click()
WebDriverWait(driver, 10).until(EC.number_of_windows_to_be(2))
new = next(h for h in driver.window_handles if h != main)
driver.switch_to.window(new)
# ... work in the new tab ...
driver.close()
driver.switch_to.window(main)   # always switch back

Wrap window work in a helper that records the original handle and always switches back in a finally block. Avoid relying on the order of window_handles; identify windows by excluding known handles or by checking their title or URL.