I'm trying to get a list of tuples, with each tuple consisting of a
directory, and a list of files. I only want a tuple if and only if the
filtered list of files is not empty. And, i want the list of files in the
tuples to be filtered. For this, i came up with the following code:
<code>
# 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?
eelco 7 1384
"Eelco Hoekema" <ee**********@xs4all.nl> wrote in message
news:pa***************************@xs4all.nl... I'm trying to get a list of tuples, with each tuple consisting of a directory, and a list of files. I only want a tuple if and only if the filtered list of files is not empty. And, i want the list of files in the tuples to be filtered. For this, i came up with the following code:
<code>
# 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?
eelco
How about,
fltres = filter(song, files)
[(root, fltres ) for (root, dir, files) in os.walk(os.path.abspath('.')) if
fltres]
Tom
Actually I think (??) this is better done in a loop:
(not tested)
toc=[]
for root, dir, files in os.walk(os.path.abspath('.')):
mp3files=[f for f in files if f.lower().endswith('.mp3')]
if mp3files: toc.append((root, mp3files))
HTH,
Larry Bates
Syscon, Inc.
"Eelco Hoekema" <ee**********@xs4all.nl> wrote in message
news:pa***************************@xs4all.nl... I'm trying to get a list of tuples, with each tuple consisting of a directory, and a list of files. I only want a tuple if and only if the filtered list of files is not empty. And, i want the list of files in the tuples to be filtered. For this, i came up with the following code:
<code>
# 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?
eelco
Larry Bates schreef: Actually I think (??) this is better done in a loop: (not tested)
toc=[] for root, dir, files in os.walk(os.path.abspath('.')): mp3files=[f for f in files if f.lower().endswith('.mp3')] if mp3files: toc.append((root, mp3files))
That is about the same as Facundo Bastida said. But then, i like this
better:
tmp = [(root, files) for (root, dir, files) in os.walk(os.path.abspath('.')) if files]
toc = [(root, files) for (root, files) tmp if filter(song, files)]
But that means 2 list comprehensions. Ans i'm just wondering if it can be
done in one, without filtering twice.
eelco
On Fri, 6 Aug 2004, Eelco Hoekema wrote: [(root, filter(song, files)) for (root, dir, files) in os.walk(os.path.abspath('.')) if filter(song, files)]
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?
You may do best to split this into two LCs:
temp = [(root, filter(song,files)) for (root, dir, files) in
os.walk(os.path.abspath('.'))]
temp = [(root, songs) for (root, songs) in temp if songs]
Or if you prefer, replace the latter with:
temp = filter(temp, lambda x: x[1])
Or even, in 2.4:
temp = filter(temp, itemgetter(1))
In 2.4, you will also be able to replace the first LC with a generator
expression, saving a bit of both memory and processor time (the change
would consist of replacing the brackets with parentheses).
Hope this helps.
Eelco Hoekema schreef: That is about the same as Facundo Bastida said. But then, i like this better:
tmp = [(root, files) for (root, dir, files) in os.walk(os.path.abspath('.')) if files] toc = [(root, files) for (root, files) tmp if filter(song, files)]
Hmm. That doesn't work. It's the other way around, like Christoffer
King showed:
tmp = [(root, files) for (root, dir, files) in os.walk(os.path.abspath('.')) if filter(song, files)]
toc = [(root, files) for (root, files) tmp if files]
eelco
Eelco> # song filter: will return true if the file seems to be an mp3 file.
Eelco> # (may not be the best way to do this)
Eelco> def song(f):
Eelco> (name, ext) = os.path.splitext(f)
Eelco> return ext.lower() == '.mp3'
Eelco> # list comprehension walking through a directory tree
Eelco> [(root, filter(song, files)) for (root, dir, files) in os.walk(os.path.abspath('.')) if filter(song, files)]
In this particular case, since song() only returns True or False, you could
use
[(root, True) for (root, dir, files) in os.walk(os.path.abspath('.'))
if filter(song, files)]
Skip
Skip Montanaro schreef: Eelco> # list comprehension walking through a directory tree Eelco> [(root, filter(song, files)) for (root, dir, files) in os.walk(os.path.abspath('.')) if filter(song, files)]
In this particular case, since song() only returns True or False,
song() does return True or False, but the return value is used in the
filter, which returns a list.
you could use
[(root, True) for (root, dir, files) in os.walk(os.path.abspath('.')) if filter(song, files)]
That would yield a list of tuples of directories that contain at least one
song. Could still be of use.
eelco This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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