In generated code you might see functions marked with @pyExtract

So what it is?

Simple - it is the marker for the python script used to extract mangling information from MS dumpbin's (or *nix 'nm' tool) output and generate replacement for those functions.

At the moment of writting the script itself is not finished yet, however you can see what it does from my another project

https://github.com/Superbelko/imgui-d/blob/master/extract.py

But why it is there?

D still has somewhat limited support for C++ name mangling schemes, certain things works better on Windows, other on *NIX, some doesn't works on either. Hence the need for such script.