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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 fold(self, **_3to2kwargs):
 policy = _3to2kwargs['policy']; del _3to2kwargs['policy'] """Fold header according to policy. The parsed representation of the header is folded according to RFC5322 rules, as modified by the policy. If the parse tree contains surrogateescaped bytes, the bytes are CTE encoded using the charset 'unknown-8bit". Any non-ASCII characters in the parse tree are CTE encoded using charset utf-8. XXX: make this a policy setting. The returned value is an ASCII-only string possibly containing linesep characters, and ending with a linesep character. The string includes the header name and the ': ' separator. """

        # At some point we need to only put fws here if it was in the source.
        header = parser.Header([
            parser.HeaderLabel([
                parser.ValueTerminal(self.name, 'header-name'),
                parser.ValueTerminal(':', 'header-sep')]),
            parser.CFWSList([parser.WhiteSpaceTerminal(' ', 'fws')]),
                             self._parse_tree])
        return header.fold(policy=policy)