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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 default_asset_manager(self):
 """ Returns the default asset manager using the current config. This is only used if asset_manager is set to None in the constructor. """

        cache_path = None
        cache_directory = self.config['CACHE_DIRECTORY']
        if cache_directory:
            cache_directory = cache_directory.format(version=__version__)
            cache_path = os.path.join(self.instance_path, cache_directory)
        return GitHubAssetManager(
            cache_path, self.config['STYLE_URLS'], self.quiet)