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If you want the best of all worlds.  Grab the text from the
underlying TypeError and append it to the higher level
message before re-raising TypeError.

I'm happy with whatever you decide to do.  When deciding, be
sure to consider bug #963956 -- it is a small disaster with
the msg appearing totally unrelated to what caused it.

And, no, the statement wasn't equivocal.  Low level routines
cannot know for all time and all situtations the context in
which they were called.  Sometimes they are fortunate and
tend to be called by only one thing or in just one context;
however, that is subject to change as soon as new high level
routine decides to use that building block.

In this particular case, the metaclass function call can
launch just about anything.  The callee really has no way of
knowing the circumstances of how it was called -- in this
case, one of the implicit actions of metaclasses.