How to transfer music onto iTunes

There are (at least) two simple ways of achieving this:

1. Select the songs in iTunes and drag them to a folder in the Finder. Copy said folder to the other computer (via WiFi, external drive, Disk Target Mode, whatever). Drag files out of folder and drop on iTunes.
2. iTunes Match. For a cost of $25 per year, you can store all your music in iCloud. Whether you bought said music from iTunes, or ripped it from CD, or got it from anywhere. Then you can access it from all your devices - iPhones, iPads, Macs, iPod Touches, AppleTVs - anything that can see iCloud.

1. check if you have relocated songs.
2. check if your files can be rewritten.

I use self-written python program to remove stale content.

import win32com.client
itunes= win32com.client.Dispatch("iTunes.Application")
ITTrackKindFile=1
mainLibrary = itunes.LibraryPlaylist
tracks = mainLibrary.Tracks
numTracks = tracks.Count
deletedTracks=0
batch_size = 90 
deleted = []
while True:
  while numTracks  !=0:
   currTrack=tracks.Item(numTracks)
   if currTrack.Kind == ITTrackKindFile:
       if currTrack.Location == "":
         deleted.append(currTrack)
   numTracks-=1
   for track in deleted:
      track.Delete()
      deletedTracks+=1
   del deleted[:] # free memory and close handles
   if not numTracks:
     break

if deletedTracks > 0:
if deletedTracks == 1:
  print "Removed 1 dead track."
else:
  print "Removed " + str(deletedTracks) + " dead tracks."
else:
  print "No dead tracks were found."