Why does formatting give an error?

Question

Python

add = 2
plural = u'недели'
comment =  u'Добавьте ещё %(add)s доп. %(plural)s.' % (add, plural)

format requires a mapping

Answer 1

comment = u'Add another %s extra. %s.' % (add, plural)
or
comment = u'Add more %(add)s extra. %(plural)s.' % ({'add': add, 'plural': plural})