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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 gzip_files(self):
 """Return a list of the files compressed by this link. This returns all files that were explicitly marked for compression. """

        ret_list = []
        for key, val in self.file_dict.items():
            # For temp files we only want files that were marked for removal
            if val & FileFlags.gz_mask:
                ret_list.append(key)
        return ret_list