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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 www_authenticate(self):
 """The `WWW-Authenticate` header in a parsed form."""

        def on_update(www_auth):
            if not www_auth and 'www-authenticate' in self.headers:
                del self.headers['www-authenticate']
            elif www_auth:
                self.headers['WWW-Authenticate'] = www_auth.to_header()
        header = self.headers.get('www-authenticate')
        return parse_www_authenticate_header(header, on_update)