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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 _str_desc(self, reader):
 """String containing information about the current GO DAG."""

        data_version = reader.data_version
        if data_version is not None:
            data_version = data_version.replace("releases/", "")
        desc = "{OBO}: fmt({FMT}) rel({REL}) {N:,} GO Terms".format(
            OBO=reader.obo_file, FMT=reader.format_version,
            REL=data_version, N=len(self))
        if reader.optobj:
            desc = "{D}; optional_attrs({A})".format(D=desc, A=" ".join(sorted(reader.optobj.optional_attrs)))
        return desc