code: def get_hosts_retriever(s=None):
      
      s = s or env.hosts_retriever
  #     #assert s, 'No hosts retriever specified.'
      if not s:
          return env_hosts_retriever
  #     module_name = '.'.join(s.split('.')[:-1])
  #     func_name = s.split('.')[-1]
  #     retriever = getattr(importlib.import_module(module_name), func_name)
  #     return retriever
      return str_to_callable(s) or env_hosts_retriever
docs: Given the function name, looks up the method for dynamically retrieving host data.