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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 same_page_choosen(form, field):
 """Check that we are not trying to assign list page itself as a child."""

    if form._obj is not None:
        if field.data.id == form._obj.list_id:
            raise ValidationError(
                _('You cannot assign list page itself as a child.'))