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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 form(self) -> Optional['HTMLFormElement']: """Get ``HTMLFormElement`` object related to this node."""

        if self.__form:
            return self.__form
        parent = self.parentNode
        while parent:
            if isinstance(parent, HTMLFormElement):
                return parent
            else:
                parent = parent.parentNode
        return None