Efficiently removing subdirectories in dirnames from os.walk

Question

On a mac in python 2.7 when walking through directories using os.walk my script goes through 'apps' i.e. appname.app, since those are really just directories of themselves. Well later on in processing I am hitting errors when going through them. I don't want to go through them anyways so for my purposes it would be best just to ignore those types of 'directories'.

So this is my current solution:

for root, subdirs, files in os.walk(directory, True):
    for subdir in subdirs:
        if '.' in subdir:
            subdirs.remove(subdir)
    #do more stuff

As you can see, the second for loop will run for every iteration of subdirs, which is unnecessary since the first pass removes everything I want to remove anyways.

There must be a more efficient way to do this. Any ideas?

Answer 1

You can do something like this (assuming you want to ignore directories containing '.'):

subdirs[:] = [d for d in subdirs if '.' not in d]

The slice assignment (rather than just subdirs = ...) is necessary because you need to modify the same list that os.walk is using, not create a new one.

Note that your original code is incorrect because you modify the list while iterating over it, which is not allowed.

Answer 2

Perhaps this example from the Python docs for os.walk will be helpful. It works from the bottom up (deleting).

# Delete everything reachable from the directory named in "top",
# assuming there are no symbolic links.
# CAUTION:  This is dangerous!  For example, if top == '/', it
# could delete all your disk files.
import os
for root, dirs, files in os.walk(top, topdown=False):
    for name in files:
        os.remove(os.path.join(root, name))
    for name in dirs:
        os.rmdir(os.path.join(root, name))

I am a bit confused about your goal, are you trying to remove a directory subtree and are encountering errors, or are you trying to walk a tree and just trying to list simple file names (excluding directory names)?