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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 addr_spec(self):
 """The addr_spec (username@domain) portion of the address, quoted according to RFC 5322 rules, but with no Content Transfer Encoding. """

        nameset = set(self.username)
        if len(nameset) > len(nameset-parser.DOT_ATOM_ENDS):
            lp = parser.quote_string(self.username)
        else:
            lp = self.username
        if self.domain:
            return lp + '@' + self.domain
        if not lp:
            return '<>'
        return lp