code: def _walk_breadth(
          self,
          fs,  # type: FS
          path,  # type: Text
          namespaces=None,  # type: Optional[Collection[Text]]
      ):
          # type: (...) -> Iterator[Tuple[Text, Optional[Info]]]
          
          queue = deque([path])
          push = queue.appendleft
          pop = queue.pop
  
          _combine = combine
          _scan = self._scan
          _calculate_depth = self._calculate_depth
          _check_open_dir = self._check_open_dir
          _check_scan_dir = self._check_scan_dir
          _check_file = self.check_file
  
          depth = _calculate_depth(path)
  
          while queue:
              dir_path = pop()
              for info in _scan(fs, dir_path, namespaces=namespaces):
                  if info.is_dir:
                      _depth = _calculate_depth(dir_path) - depth + 1
                      if _check_open_dir(fs, dir_path, info):
                          yield dir_path, info  # Opened a directory
                          if _check_scan_dir(fs, dir_path, info, _depth):
                              push(_combine(dir_path, info.name))
                  else:
                      if _check_file(fs, info):
                          yield dir_path, info  # Found a file
              yield dir_path, None
docs: Walk files using a *breadth first* search.