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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 upload_documentation(self, metadata, doc_dir):
 """ Upload documentation to the index. :param metadata: A :class:`Metadata` instance defining at least a name and version number for the documentation to be uploaded. :param doc_dir: The pathname of the directory which contains the documentation. This should be the directory that contains the ``index.html`` for the documentation. :return: The HTTP response received from PyPI upon submission of the request. """

        self.check_credentials()
        if not os.path.isdir(doc_dir):
            raise DistlibException('not a directory: %r' % doc_dir)
        fn = os.path.join(doc_dir, 'index.html')
        if not os.path.exists(fn):
            raise DistlibException('not found: %r' % fn)
        metadata.validate()
        name, version = metadata.name, metadata.version
        zip_data = zip_dir(doc_dir).getvalue()
        fields = [(':action', 'doc_upload'),
                  ('name', name), ('version', version)]
        files = [('content', name, zip_data)]
        request = self.encode_request(fields, files)
        return self.send_request(request)