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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 hash(self):
 """Provide access to the complete hash string. The hash string may have zero or more hash values with appropriate prefixes. All hash values are assumed to be strings """

        hashvals = []
        if (self.md5 is not None):
            hashvals.append('md5:' + self.md5)
        if (self.sha1 is not None):
            hashvals.append('sha-1:' + self.sha1)
        if (self.sha256 is not None):
            hashvals.append('sha-256:' + self.sha256)
        if (len(hashvals) > 0):
            return(' '.join(hashvals))
        return(None)