For a large collection of MP3s, what you can do is put all of the songs of one artist in a particular folder. Eg:- All "Coldplay" songs go in the "Coldplay" folder
If you are on Linux, you can do the following:-
import os
import eyed3
folder = raw_input('Please enter the folder of music')
files = os.listdir(folder) # This will give us a list of all of the MP3s in that folder
artist = folder.split('/')[-1]
for x in files:
mp3 = eyed3.load(folder + '/' + x) # Loads each and every MP3
mp3.tag.artist = unicode(artist, "UTF-8") # Sets the "artist" tag to the artist name
mp3.tag.save() # Saves tag
Just edit the code by making all the slashes "/" into backslashes "\" if you are on Windows
The above code works pretty well for me. Glad if I helped :)