Order of filenames from os.listdir

Question

Assume that folder A contains the following files:

0.jpg
1.jpg
2.jpg
.
.
.
n.jpg
.
.
.

Now, a python script looks into folder A and using

for path, dirs, files in os.walk(path_to_A):
    for filename in files:
        fullpath = os.path.join(path, filename)

reads the filename (reads each image) and updates an array B. The size of array B is exactly that of the number of images inside A.

My question is, will it ALWAYS be the case that the j-th position of the array will correspond to the j.jpg image file?

For example if the names inside folder A differ ( but are sorted in the lexicographic order - btw, is it really the lexicographic order that is preserved when we list a directory in win or linux OS? ) will this be depicted in array B?

Thanks!

score 5 · Accepted Answer · answered Jun 29 '16 at 15:44

No, the j-th position will (or at least CAN) vary. From the docs (emphasis mine)

os.listdir(path='.')
Return a list containing the names of the entries in the directory given by path. The list is in arbitrary order, and does not include the special entries '.' and '..' even if they are present in the directory.

That said, if you want it sorted, sorted produces a stable lexicographically sorted list. sorted(os.listdir("your/path/here"))[n] should always point to the n-th file (unless your directory changes contents!)

`sorted` will be lexically stable, but keep in mind that it's case sensitive. So `A.jpg` and `a.jpg` will be nowhere near each other, and `C.jpg` will show up before `b.jpg`. There's also issues like `1.jpg` vs. `02.jpg`. — jpmc26, Jun 29 '16 at 16:27

score 0 · Answer 2 · answered Aug 22 '18 at 14:00

Original Author: Elliot's on this thread

Use natsort library:

Install the library with the following command for Ubuntu and other Debian versions

Python 2

sudo pip install natsort

Python 3

sudo pip3 install natsort

Details of how to use this library is found here

Order of filenames from os.listdir

2 Answers2