How to tell in site.py if python is being invoked interactively?

[Alex]

> There seems to be a C global variable "Py_InteractiveFlag", which
> could probably be got at with a C extension; so if you're writing one
> of those anyway, this shouldn't be too much of a stretch.  If you're
> not, dunno, sorry.

Yeah, that might be a good idea.  I'll probably write such a thing at
some stage.  Thanks.

Alex.