python - How to access var within function but outside subfunction -

i have following function, includes function inside it:

def function():     previously_parsed_tv_urls = set()      def _get_all_related(tv_urls):          api_urls = [self._build_api_url_from_store_url(url)                     url in tv_urls not in previously_parsed_tv_urls]         previously_parsed_tv_urls = tv_urls.union(api_urls)       function() 

however, don't have access previously_parsed_tv_urls. how access within _get_all_related function?

here error get:

unboundlocalerror: local variable 'previously_parsed_tv_urls' referenced before assignment 

if want reference earlier defined name, in "higher" scope, python fine it. grants sorts of power, when you're messing around in interpreter.

however, python pretty generous @ trying stop doing things can bite or cause nasty, difficult debug problems. unboundlocalerror comes in.

as redefine name in particular scope, python marks local scope (only), , not higher provide value. keeps accidentally mucking higher scopes without explicitly requesting it.

as andrea corbellini mentioned, python 3 adds nonlocal keyword permit make such explicit request. pep 3104 pretty exhaustively describes change in scoping rules permits, comparing both python without nonlocal other common languages of kind.