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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 sequence(self):
 """Returns the sequence of the `Polynucleotide` as a string. Returns ------- sequence : str String of the monomer sequence of the `Polynucleotide`. """

        seq = [x.mol_code for x in self._monomers]
        return ' '.join(seq)