'Constructor.
Args:
base_fd: A handler to the predecessor handler.
pathspec: The pathspec to open.
progress_callback: A callback to indicate that the open call is still
working but needs more time.
full_pathspec: The full pathspec we are trying to open.
Raises:
IOError: if this handler can not be instantiated over the
requested path.'

def __init__(self, base_fd, pathspec=None, progress_callback=None, full_pathspec=None):

    _ = pathspec
    _ = full_pathspec
    self.base_fd = base_fd
    self.progress_callback = progress_callback
    if (base_fd is None):
        self.pathspec = rdf_paths.PathSpec()
    else:
        self.pathspec = base_fd.pathspec.Copy()
    self.metadata = {}
