Processing files in sorted order

I have 67 images in a directory with names as:

Im_2601_0 Im_2601_1 Im_2601_4 Im_2601_8 Im_2601_16 Im_2601_32 Im_2601_64 Im_2601_128 Im_2601_256

Im_2602_0 Im_2602_1 Im_2602_4 Im_2602_8 Im_2602_16 Im_2602_32 Im_2602_64 Im_2602_128 Im_2602_256

Im_2603_0 Im_2603_1 Im_2603_4 Im_2603_8 Im_2603_16 Im_2603_32 Im_2603_64 Im_2603_128 Im_2603_256
.
.
.
.
.
.
.
.
.
Im_26067_0 Im_26067_1 Im_26067_4 Im_26067_8 Im_26067_16 Im_26067_32 Im_26067_64 Im_26067_128 Im_26067_256

Files are jpg files Im_260x_y where x is the number of images 1..67, y are 0, 1, 4, 8, 16, 32, 64, 128, 258. These files are randomly stored in the directory.

I want to process the files in sorted order (same order which I have written above i.e Image 1 for all of 0, 1, 4, 8, 16, 32, 64, 128, 258. Then image 2 for all of 0, 1, 4, 8, 16, 32, 64, 128, 258 and so on).

How can I write Python code for this?

Answer

You could do this:

from glob import glob
from os import path

DIRECTORY = '.' # directory containing image files
PREFIX = '260'

def process(filename):
    print(filename) # do your real processing here

def getkey(s):
    t = path.basename(s).split('_')
    assert len(t) == 3
    assert t[1].startswith(PREFIX)
    a = t[1][len(PREFIX):]
    b, _ = path.splitext(t[2])
    try:
        return int(a), int(b)
    except ValueError:
        return 0, 0


filelist = glob(path.join(DIRECTORY, 'Im_*'))

for file in sorted(filelist, key=getkey):
    process(file)