code: def function_selectors(self) -> Iterable[bytes]:
          
          selectors = self._function_signatures_by_selector.keys()
          if self._fallback_function_abi_item is None:
              return tuple(selectors)
          return (*selectors, self.fallback_function_selector)
docs: The selectors of all normal contract functions,
          plus ``self.fallback_function_selector`` if the contract has a non-default fallback function.