A more intelligent .sort()?

[snippsat]

There is names for these problems human or natural sort.
@DeaD_EyE solution look fine.
There also libraries for this natsort.
Testing natsort with code from DeaD_EyE.

# pip install natsort
>>> from natsort import natsorted
>>> 
>>> natsorted(lst)
['pdf_1_page1',
 'pdf_1_page2',
 'pdf_1_page3',
 'pdf_1_page4',
 'pdf_2_page1',
 'pdf_2_page2',
 'pdf_2_page3',
 'pdf_2_page4',
 'pdf_3_page1',
 'pdf_3_page2',
 'pdf_3_page3',
 'pdf_3_page4',
 'pdf_4_page1',
 'pdf_4_page2',
 'pdf_4_page3',
 'pdf_4_page4',
 'pdf_5_page1',
 'pdf_5_page2',
 'pdf_5_page3',
 'pdf_5_page4',
 'pdf_6_page1',
 'pdf_6_page2',
 'pdf_6_page3',
 'pdf_6_page4',
 'pdf_7_page1',
 'pdf_7_page2',
 'pdf_7_page3',
 'pdf_7_page4',
 'pdf_8_page1',
 'pdf_8_page2',
 'pdf_8_page3',
 'pdf_8_page4',
 'pdf_9_page1',
 'pdf_9_page2',
 'pdf_9_page3',
 'pdf_9_page4',
 'pdf_10_page1',
 'pdf_10_page2',
 'pdf_10_page3',
 'pdf_10_page4']