def init_app(self, app):
if not hasattr(app, '<STR_LIT>'):<EOL><INDENT>app.extensions = {}<EOL><DEDENT>config = app.extensions.setdefault('<STR_LIT>', {})<EOL>config['<STR_LIT>'] = {}<EOL>config['<STR_LIT>'] = self.whoosheers<EOL>config['<STR_LIT>'] = app.config.get('<STR_LIT>', '<STR_LIT>') or '<STR_LIT>'<EOL>config['<STR_LIT>'] = app.config.get('<STR_LIT>', <NUM_LIT:2>)<EOL>config['<STR_LIT>'] = app.config.get('<STR_LIT>', <NUM_LIT:3>)<EOL>config['<STR_LIT>'] = app.config.get("<STR_LIT>", False)<EOL>config['<STR_LIT>'] = app.config.get('<STR_LIT>', True)<EOL>if app.config.get('<STR_LIT>', None) is not None:<EOL><INDENT>warnings.warn(WhoosheeDeprecationWarning("<STR_LIT>"))<EOL>config['<STR_LIT>'] = app.config.get('<STR_LIT>')<EOL><DEDENT>if not os.path.exists(config['<STR_LIT>']):<EOL><INDENT>os.makedirs(config['<STR_LIT>'])<EOL><DEDENT>
Initialize the extension. It will create the `index_path_root`
        directory upon initalization but it will **not** create the index.
        Please use :meth:`reindex` for this.

        :param app: The application instance for which the extension should
                    be initialized.