[Newby question] List comprehension

[Batista, Facundo]

[Eelco Hoekema]

#- # song filter: will return true if the file seems to be an mp3 file. 
#- # (may not be the best way to do this)
#- def song(f):
#-     (name, ext) = os.path.splitext(f)
#-     return ext.lower() == '.mp3'
#- 
#- # list comprehension walking through a directory tree
#- [(root, filter(song, files)) for (root, dir, files) in 
#- os.walk(os.path.abspath('.')) if filter(song, files)]
#- 
#- 
#- </code>
#- 
#- Now, this will work. However, it seems kind of silly to call 
#- the filter
#- twice. Is there a way to keep this in one list 
#- comprehension, but with
#- just filtering once?

files = []
for (root, dir, files) in os.walk(os.path.abspath('.')):
	mp3files = filter(song, files)
	if mp3files:
		files.append((root, mp3files))


Now, explain me why a list comprehension is better here.

.	Facundo