Name of files opened by a process in window?

Question

How to print name of file open by some process (PID) in window? Or All Processes (PID) currently open a file.
Process Explorer is a utility works for same. But how does it work not mentioned? Any /proc filesystem kind of thing present in windows?

Can we read any Window's Registry?  
I wants to write a programming code And I rarely work on windows. 

Got two solutions in Python:
1. import psutil
2. import win32api, win32con, win32process

But it is still a question to me!
1. How does these libraries works?
2. Any register, memory or virtual file system keeps this information?

If its possible in window, Why this information not present in TasK-Manager?

Answer 1

Here is the platform independent solution in python.

   import psutil
   p = psutil.Process(os.getpid()) # or PID of process
   p.open_files()

So i refer you psutil package it has too good functions for getting information on running processes

Answer 2

Here's a way to get a filename from pid using the Win32 API:

import win32api, win32con, win32process

handle = win32api.OpenProcess(win32con.PROCESS_ALL_ACCESS, False, pid) #get handle for the pid
filename = win32process.GetModuleFileNameEx(handle, 0) #get exe path & filename for handle

This works on windows only (obviously).