Hello,
the boundary attribute of the Shape instance is not accessible through the Python API. Instead it seems to be bounded to the type attribute :
>>> shape.boundary = PhotoScan.Shape.OuterBoundary
2017-02-03 14:58:46 Traceback (most recent call last):
2017-02-03 14:58:46 File "<console>", line 1, in <module>
2017-02-03 14:58:46 TypeError: value must be PhotoScan.Shape.Type, not
>>> shape.type
2017-02-03 15:01:05 PhotoScan.Shape.Type.Polygon
>>> shape.boundary
2017-02-03 15:01:09 PhotoScan.Shape.Type.Polygon