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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 union(self, other: 'FileLineSet') -> 'FileLineSet': """ Returns a set of file lines that contains the union of the lines within this set and a given set. """

        # this isn't the most efficient implementation, but frankly, it doesn't
        # need to be.
        assert isinstance(other, FileLineSet)
        l_self = list(self)
        l_other = list(other)
        l_union = l_self + l_other
        return FileLineSet.from_list(l_union)