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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 cache_entry(self):
 """ Returns a CacheEntry instance for File. """

        if self.storage_path is None:
            raise ValueError('This file is temporary and so a lal '
                             'cache entry cannot be made')

        file_url = urlparse.urlunparse(['file', 'localhost', self.storage_path, None,
                                            None, None])
        cache_entry = lal.utils.CacheEntry(self.ifo_string,
                   self.tagged_description, self.segment_list.extent(), file_url)
        cache_entry.workflow_file = self
        return cache_entry