why i don't like os.walk()

[Skaperen]

so ...

the [:] on the LHS uses a whole list slice assignment to update the existing reference and avoid assigning a new reference. and each dirlist reference i get from each step of the generator i get from os.walk() is kept internal in the generator and subsequently used, as modified in-place, to descend in the tree walk.

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Well, if I want to traverse my /home/$USER directory and I want to exclude Music and Video I can just remove them from the list:

for root, dirs, files in os.walk('/home/victor/'):
    dirs = [item for item in dirs[:] if item not in ('Music', 'Video)]

It's completely safe to do that and os.walk will not going through these directories.

so ...

for root, dirs, files in os.walk('/home/victor/'):
    dirs[:] = [item for item in dirs if item not in ('Music', 'Video)]

it builds a new list without those 2 names, which is thus 2 elements shorter, and is copied (because of the slice reference on the LHS) into the whole list (because the slice reference is a whole reference) making that list to now be 2 elements shorter.

or i could do ...

for root, dirs, files in os.walk('/home/victor/'):
    dirs[:] = sorted([item for item in dirs if item not in ('Music', 'Video)])