python selenium unable to select element - selenium

Question

I'm trying to select below element in a webpage.
.active > b:nth-child(1)
This is my code :
timbro = browser.find_element_by_css_selector('.active > b:nth-child(1)')
hover = ActionChains(browser).move_to_element(timbro)
hover.perform()
This is part of the error I'm getting:
Message: Unable to locate element:
{"method":"css selector","selector":".active > b:nth-child(1)"}"
what I'm trying to do is activate a drop down menu so that I can click on another link.
HTML Snippet:
<li>
<b>Menu iniziale</b>
<ul style="display: block;" class="sub-links">
<li>
Anagrafica
</li>
<li>
Fine sessione
</li>
<li>
Home
</li>
<li>
Timbro
</li>
</ul>
</li>

Answer 1

You should try using WebDriverWait to wait until presence of element as below :-
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
wait = WebDriverWait(browser, 5)
menuIniziale = wait.until(EC.presence_of_element_located((By.LINK_TEXT, "Menu iniziale")))
hover = ActionChains(browser).move_to_element(menuIniziale).move_to_element(wait.until(EC.presence_of_element_located((By.LINK_TEXT, "Timbro"))))
hover.click().build().perform()
Edited1 :- If unfortunately LINK_TEXT does not work try using XPATH as below :-
menuIniziale = wait.until(EC.presence_of_element_located((By.XPATH, ".//a[contains(.,'Menu iniziale')]")))
hover = ActionChains(browser).move_to_element(menuIniziale).move_to_element(wait.until(EC.presence_of_element_located((By.XPATH, ".//a[contains(.,'Timbro')]"))))
hover.click().build().perform()
Or try using CSS_SELECTOR as below :-
menuIniziale = wait.until(EC.presence_of_element_located((By.CSS_SELECTOR, "a.main-link")))
hover = ActionChains(browser).move_to_element(menuIniziale).move_to_element(wait.until(EC.presence_of_element_located((By.CSS_SELECTOR, "ul.sub-links > li:nth-child(4)"))))
hover.click().build().perform()
Edited2 : If this element is inside an iframe, you need to switch that iframe before finding element as below :-
wait.until(EC.frame_to_be_available_and_switch_to_it(("frame name or id")))
#Now after successfully switching to frame do any one of the above steps
Edited3 :- If you are now able to open menu but not able to select subMenu try as below :-
wait.until(EC.frame_to_be_available_and_switch_to_it(("frame name or id")))
menuIniziale = wait.until(EC.presence_of_element_located((By.CSS_SELECTOR, "a.main-link")))
hover = ActionChains(browser).move_to_element(menuIniziale)
hover.build().perform()
subMenu = wait.until(EC.visibility_of_element_located((By.XPATH, ".//a[contains(.,'Timbro')]")))
subMenu.click()
Edited4: Final code
menuIniziale = wait.until(EC.presence_of_element_located((By.XPATH, ".//a[contains(.,'Menu iniziale')]")))
hover = ActionChains(browser).move_to_element(menuIniziale)
hover.perform()
subMenu = wait.until(EC.visibility_of_element_located((By.XPATH, ".//a[contains(.,'Timbro')]")))
subMenu.click()
hover = ActionChains(browser).move_to_element(subMenu)
hover.click().perform()