a)
from selenium.common.exceptions import NoSuchElementException
def check_exists_by_xpath(xpath):
try:
webdriver.find_element_by_xpath(xpath)
except NoSuchElementException:
return False
return True
b) use xpath – the most reliable. Moreover you can take the xpath as a standard throughout all your scripts and create functions as above mentions for universal use.
UPDATE: I wrote the initial answer over 4 years ago and at the time I thought xpath would be the best option. Now I recommend to use css selectors. I still recommend not to mix/use “by id”, “by name” and etc and use one single approach instead.