Wouldn't it make sense to expose this object in Python, e.g. by contructing it from a dictionary of string mappings ?
(The type constructor is not made available in bltinmodule.c.)
No. AFAIR, this idea was explicitly rejected at the time the patch was designed (see the comments on the stat patch for the exact history).
The rationale was that it is easy enough to create a class that doubles as tuple in Python yourself (perhaps through inheritance from tuple), so there would be no need to expose this type.