docs: def set_lock(fname):
      """
      Try to lock file and write PID.
      
      Return the status of operation.
      """
      
      global fh
      fh = open(fname, 'w')
  
      if os.name == 'nt':
          # Code for NT systems got from: http://code.activestate.com/recipes/65203/
          
          import win32con
          import win32file
          import pywintypes
          
          LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
          LOCK_SH = 0 # the default
          LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
          
          # is there any reason not to reuse the following structure?
          __overlapped = pywintypes.OVERLAPPED()
          
          hfile = win32file._get_osfhandle(fh.fileno())
          try:
              win32file.LockFileEx(hfile, LOCK_EX | LOCK_NB, 0, -0x10000, __overlapped)
          except pywintypes.error as exc_value:
              # error: (33, 'LockFileEx', 'The process cannot access 
              # the file because another process has locked a portion
              # of the file.')
              if exc_value[0] == 33:
                  return False
      else:
          from fcntl import flock, LOCK_EX, LOCK_NB
          try:
              flock(fh.fileno(), LOCK_EX | LOCK_NB)
          except Exception as ex:
              return False
      
      fh.write(str(os.getpid()))
      fh.flush()
      return True