python - If thing exists, do something with thing -

what correct (pythonic) way this?

var = 'the quick brown fox'  def exists(query, string):     if query in string:         return query     else:         return none  if thing = exists('fox', var):     print(thing.upper()) 

this example, i'm trying check if selenium web element exists. want avoid setting result variable because defeats purpose of "exists". also, don't want perform search twice returning true/false first time , again, if it's true, it.

this 1 of cases there's more 1 way it. few things do:

1. treat result collection of 0 1 elements (it makes more sense if call find_one in such cases):

   def find_one(query, string):     if query in string:         return [query]     return [] 

   then can use function in for loop:

   for existing_element in find_one(query, string):     # existing element     break else:     # here if don't have elements (note `break` above) 

2. pass callback first argument:

   def if_exists(cb, query, string):     if query in string:         cb(query)  def run_on_valid_query(q):     # q  if_exists(run_on_valid_query, query, string) 

3. bite bullet , use intermediate variable:

   result = extract_from(query, string) if result:  # work here