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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 _package_top_dir(self):
 """ Find one or more directories that we think may be the top-level directory of the package; return a list of their absolute paths. :return: list of possible package top-level directories (absolute paths) :rtype: list """

        r = [self.package_dir]
        for l in self._pip_locations:
            if l is not None:
                r.append(l)
        for l in self._pkg_resources_locations:
            if l is not None:
                r.append(l)
        return sorted(list(set(r)))