Check if any alert exists using selenium with python

I'm trying to write a test with selenium in python language for a web page that manages users. In this page someone can add role for users and if a role exists while adding it, an alert raises. I don't know if the alert is a javascript alert or an element of the web page. I want to automatically check the existence of the alert, because checking for the role in the list wastes time and has an enormous load. I tried this:

browser = webdriver.Firefox()
browser.get("url")
browser.find_the_element_by_id("add_button").click()
try:
    alert = browser.switch_to_alert()
    alert.accept()
    print "alert accepted"
except:
    print "no alert"

But it didn't work and I got the "UnexpectedAlertPresentException". I also tried this:

browser = webdriver.Firefox()
browser.get("url")
browser.find_the_element_by_id("add_button").click()
s = set(browser.window_handles)
s.remove(browser.current_window_handle)
browser.switch_to_window(s.pop()) 

But I got the same exception. Additionally, I tried to access the alert with firebug to check if I can get access with its properties, but right click was disabled. I need a solution very quickly, even in other languages. I can understand the approach anyway. I will appreciate any help.

What I do is to set a conditional delay with WebDriverWait just before the point I expect to see the alert, then switch to it, like this:

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

browser = webdriver.Firefox()
browser.get("url")
browser.find_element_by_id("add_button").click()

try:
    WebDriverWait(browser, 3).until(EC.alert_is_present(),
                                   'Timed out waiting for PA creation ' +
                                   'confirmation popup to appear.')

    alert = browser.switch_to.alert
    alert.accept()
    print("alert accepted")
except TimeoutException:
    print("no alert")

WebDriverWait(browser,3) will wait for at least 3 seconds for a supported alert to appear.