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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _preprocess_add_items(self, items):
 """ Split the items into two lists of path strings and BaseEntries. """

        paths = []
        entries = []

        for item in items:
            if isinstance(item, string_types):
                paths.append(self._to_relative_path(item))
            elif isinstance(item, (Blob, Submodule)):
                entries.append(BaseIndexEntry.from_blob(item))
            elif isinstance(item, BaseIndexEntry):
                entries.append(item)
            else:
                raise TypeError("Invalid Type: %r" % item)
        # END for each item
        return (paths, entries)