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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 add_filtered_folder(self, path, regex, depth=None, source_type=DefaultSourceType):
 """ Add a folder source to scan recursively, with a regex filter on directories. :param regex: regex string to filter folders by. :param depth: if provided will be depth limit. 0 = first level only. :param source_type: what to return; files only, folders only, or both. """

        self.add_source(FilteredFolderSource(path, regex, depth, **source_type))
        return self