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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 list_lib(self, repo):
 """Return package lists """

        packages = ""
        if repo == "sbo":
            if (os.path.isfile(
                    self.meta.lib_path + "{0}_repo/SLACKBUILDS.TXT".format(
                        repo))):
                packages = Utils().read_file(self.meta.lib_path + "{0}_repo/"
                                             "SLACKBUILDS.TXT".format(repo))
        else:
            if (os.path.isfile(
                    self.meta.lib_path + "{0}_repo/PACKAGES.TXT".format(repo))):
                packages = Utils().read_file(self.meta.lib_path + "{0}_repo/"
                                             "PACKAGES.TXT".format(repo))
        return packages