new_contents: 
  try:
    from mathutils import Matrix, Vector
  except ImportError:
    # We don't have mathutils. Make some very basic replacements.
    class Vector(tuple):
      def __repr__(self):
        return "Vector({})".format(super(Vector, self).__repr__())
    class Matrix(tuple):
      def transposed(self):
        cols = [[self[j][i] for j in range(len(self))] for i in range(len(self))]
        return Matrix(cols)
      def __repr__(self):
        return "Matrix({})".format(super(Matrix, self).__repr__())
  
subject: Add previously-missed placeholder Vector/Matrix code