Walks down the root directory looking for Dvcfiles,
        skipping the directories that are related with
        any SCM (e.g. `.git`), DVC itself (`.dvc`), or directories
        tracked by DVC (e.g. `dvc add data` would skip `data/`)

        NOTE: For large repos, this could be an expensive
              operation. Consider using some memoization.

def stages(self, from_directory=None, check_dag=True):
        """
        Walks down the root directory looking for Dvcfiles,
        skipping the directories that are related with
        any SCM (e.g. `.git`), DVC itself (`.dvc`), or directories
        tracked by DVC (e.g. `dvc add data` would skip `data/`)

        NOTE: For large repos, this could be an expensive
              operation. Consider using some memoization.
        """
        from dvc.stage import Stage

        if not from_directory:
            from_directory = self.root_dir
        elif not os.path.isdir(from_directory):
            raise TargetNotDirectoryError(from_directory)

        stages = []
        outs = []

        ignore_file_handler = DvcIgnoreFileHandler(self.tree)
        for root, dirs, files in self.tree.walk(
            from_directory, ignore_file_handler=ignore_file_handler
        ):
            for fname in files:
                path = os.path.join(root, fname)
                if not Stage.is_valid_filename(path):
                    continue
                stage = Stage.load(self, path)
                for out in stage.outs:
                    outs.append(out.path + out.sep)
                stages.append(stage)

            def filter_dirs(dname, root=root):
                path = os.path.join(root, dname)
                if path in (self.dvc_dir, self.scm.dir):
                    return False
                for out in outs:
                    if path == os.path.normpath(out) or path.startswith(out):
                        return False
                return True

            dirs[:] = list(filter(filter_dirs, dirs))

        if check_dag:
            self.check_dag(stages)

        return stages