Assuming there's just one number in each file name:
>>> dirFiles = ['Picture 03.jpg', '02.jpg', '1.jpg']
>>> dirFiles.sort(key=lambda f: int(filter(str.isdigit, f)))
>>> dirFiles
['1.jpg', '02.jpg', 'Picture 03.jpg']
A version that also works in Python 3:
>>> dirFiles.sort(key=lambda f: int(re.sub('D', '', f)))
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