[Jeremy Hylton]
>  What's a sequence then?  If you say anything that PySequence_Check()
>  says okay for, then there is almost no code that accepts a sequence.

?  Isn't that backwards?  PySequence_Check() says "yes" to every instance,
and in 2.2 even says "yes" to dictionaries too (because Guido filled in
PyDict_Type's tp_as_sequence slot in order to get at sq_contains).