I want to program a virtual file system in Windows with Python.
That is, a program in Python whose interface is actually an "explorer windows". You can create & manipulate file-like objects but instead of being created in the hard disk as regular files they are managed by my program and, say, stored remotely, or encrypted or compressed or versioned, or whatever I can do with Python.
What is the easiest way to do that?
If you are trying to write a virtual file system (I may misunderstand you) - I would look at a container file format. VHD is well documented along with HDI and (embedded) OSQ. There are basically two things you need to do. One is you need to decide on a file/container format. After that it is as simple as writing the API to manipulate that container. If you would like it to be manipulated over the internet, pick a transport protocol then just write a service (would would emulate a file system driver) that listens on a certain port and manipulates this container using your API
Does it need to be Windows-native? There is at least one protocol which can be both browsed by Windows Explorer, and served by free Python libraries: FTP. Stick your program behind pyftpdlib and you're done.
While perhaps not quite ripe yet (unfortunately I have no first-hand experience with it), pywinfuse looks exactly like what you're looking for.