> but there is a catch -- the arguments should be a C int

Or a type that promotes to int. If you pass a C short or char, or a C++ bool, it is implicitly promoted to int.

> so you will need to write "expr ? 1 : 0"

Or alternatively "!!expr"

> which is not much better than "expr ? Py_True : Py_False"

I had to write that recently after reading through the Py_BuildValue docs twice to make sure I wasn't missing a format code I could use. It's a strange omission, especially because 'p' exists for PyArg_Parse. I'd very much like to see this change.