When does a binary extension gets the file extension '.pyd' and when is it '.so'

[llothar]

Thanks, my question was not how can i make python to it find. I don't
have a problem.

My question was: Why does setup.py generated sometimes a pyd and
sometimes a so file?

There must be a rule behind this.

Unforunately setup.py is not well documented. Here i mean i need a
specification not a
tutorial, because i want to know something not do something.

Don't ask why i need to know: I need to know. And maybe somebody here
can drop a
line before i have to dig around in the source code.