files = ['PresserInc-1.jpg', 'PresserInc-1_10.jpg', 'PresserInc-1_11.jpg', 'PresserInc-10.jpg', 'PresserInc-2.jpg', 'PresserInc-3.jpg', 'PresserInc-4.jpg', 'PresserInc-5.jpg', 'PresserInc-6.jpg', 'PresserInc-11.jpg']
 
import re
 
def natural_sort(l): 
    convert = lambda text: int(text) if text.isdigit() else text.lower() 
    alphanum_key = lambda key: [ convert(c) for c in re.split('([0-9]+)', key) ] 
    return sorted(l, key = alphanum_key)
 
print natural_sort(files)

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