code: def flag(self, key, env=None):
          
          env = env or self.ENVVAR_PREFIX_FOR_DYNACONF or "DYNACONF"
          with self.using_env(env):
              value = self.get_fresh(key)
              return value is True or value in true_values
docs: Feature flagging system
          write flags to redis
          $ dynaconf write redis -s DASHBOARD=1 -e premiumuser
          meaning: Any premium user has DASHBOARD feature enabled
  
          In your program do::
  
              # premium user has access to dashboard?
              >>> if settings.flag('dashboard', 'premiumuser'):
              ...     activate_dashboard()
  
          The value is ensured to be loaded fresh from redis server
  
          It also works with file settings but the recommended is redis
          as the data can be loaded once it is updated.
  
          :param key: The flag name
          :param env: The env to look for