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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 codon2weight(self, codon):
 """ Turn a codon of "000" to "999" to a number between -5.0 and 5.0. """

        length = len(codon)
        retval = int(codon)
        return retval/(10 ** (length - 1)) - 5.0