def read_file(self, filename):
        """
        :raises IOError: passed from any file operations that fail.
        """
        self.pack = {}
        with open(filename, "r") as f:
            for line in f:
                line = line.strip()
                if (len(line) == 0) or (line[0] == "#"):
                    continue
                try:
                    self._parse_modulus(line)
                except:
                    continue