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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 html(self):
 """ Build HTML documentation. """

        ret_code = self._sphinx_build('html')
        zip_fname = os.path.join(BUILD_PATH, 'html', 'pandas.zip')
        if os.path.exists(zip_fname):
            os.remove(zip_fname)

        if self.single_doc_html is not None:
            self._open_browser(self.single_doc_html)
        else:
            self._add_redirects()
        return ret_code