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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 load_index(self, version_string):
 """Load the completion index for a given CLI version. :type version_string: str :param version_string: The AWS CLI version, e.g "1.9.2". :raises: :class:`IndexLoadError <exceptions.IndexLoadError>` """

        filename = self._filename_for_version(version_string)
        try:
            contents = self._fslayer.file_contents(filename)
        except FileReadError as e:
            raise IndexLoadError(str(e))
        return contents