code: def default_from_address(self):
          
          if self._coinbase_cache_til is not None:
              if time.time - self._coinbase_cache_til > 30:
                  self._coinbase_cache_til = None
                  self._coinbase_cache = None
  
          if self._coinbase_cache is None:
              self._coinbase_cache = self.get_coinbase()
  
          return self._coinbase_cache
docs: Cache the coinbase address so that we don't make two requests for every
          single transaction.