title: presence_of_element_located by class
body: <p>I'm using python and selenium and when I try to locate an error generated by the javascript (failed login message)</p>
  
  <p>but since it takes a few moments I need to wait for presence by class.</p>
  
  <p>but this By.Class doesn't exist and I only have class in my login.</p>
  
  <pre><code>try_login(driver,'admin99','123')
  WebDriverWait(driver, 5).until(
      EC.presence_of_element_located((By.CSS_SELECTOR,"alert"))
  )
  x = driver.find_element_by_id('alert')
  </code></pre>