Kind of puzzled about timestamps

[Bruce Labitt]

This is an odd question.  It involves both python and linux.

Have a bunch of files in a directory that I'd like like to sort by 
similar names and in time order.  This isn't particularly difficult in 
python.  What is puzzling me is the modified timestamp returned by 
python doesn't match whats reported by the file manager nautilus or even 
ls.  (ls and nautilus are consistent)

$ lsb_release -d Ubuntu 20.04.2 LTS
$ nautilus --version  GNOME nautilus 3.36.3

$ python3 --version Python 3.8.5

$ ls -lght

total 4.7M
-rw-r--r-- 1 bruce 209K Feb 26 01:49 20210226_022134_PLD.edf
-rw-r--r-- 1 bruce  65K Feb 26 01:49 20210226_022134_SAD.edf
-rw-r--r-- 1 bruce 2.4M Feb 26 01:49 20210226_022133_BRP.edf
-rw-r--r-- 1 bruce 1.1K Feb 26 00:58 20210225_224134_EVE.edf
-rw-r--r-- 1 bruce 1.9M Feb 25 21:18 20210225_224141_BRP.edf
-rw-r--r-- 1 bruce 169K Feb 25 21:17 20210225_224142_PLD.edf
-rw-r--r-- 1 bruce  53K Feb 25 21:17 20210225_224142_SAD.edf

Python3 script

#!/usr/bin/env python3
import os
from datetime import datetime

def convert_date(timestamp):
   d = datetime.utcfromtimestamp(timestamp)
   formatted_date = d.strftime('%d %b %Y  %H:%M:%S')
   return formatted_date

with os.scandir('feb262021') as entries:
   for entry in entries:
     if entry.is_file():
       info = entry.stat()
       print(f'{entry.name}\t Last Modified: 
{convert_date(info.st_mtime) }' )  # last modification

info /(after exit) contains/: os.stat_result(st_mode=33188, 
st_ino=34477637, st_dev=66306, st_nlink=1, st_uid=1000, st_gid=1000, 
st_size=213416, st_atime=1614379184, st_mtime=1614322176, 
st_ctime=1614379184)

Running the script results in:

20210226_022133_BRP.edf     Last Modified: 26 Feb 2021  06:49:34
20210225_224141_BRP.edf     Last Modified: 26 Feb 2021  02:18:42
20210225_224142_PLD.edf     Last Modified: 26 Feb 2021  02:17:44
20210225_224142_SAD.edf     Last Modified: 26 Feb 2021  02:17:44
20210225_224134_EVE.edf     Last Modified: 26 Feb 2021  05:58:26
20210226_022134_SAD.edf     Last Modified: 26 Feb 2021  06:49:36
20210226_022134_PLD.edf     Last Modified: 26 Feb 2021  06:49:36

Actually, what is returned by my script is at least sensible, given that 
20210225_224141_BRP.edf started on Feb 25th and ended recording at 
2:17am on Feb 26th.  I know this because I can see the data on a 
separate program. 20210226_022133_BRP.edf started on Feb 26th at around 
2:21am and terminated at 6:49am.  BRP files are written to continuously 
at a 25 Hz rate all evening.  What makes no sense whatsoever is what 
*ls* is reporting.

Do *ls* and python3 use different definitions of "last modified"?

Guess I can keep going, but I really was surprised at the difference 
between methods.  Default for ls is "last modified", at least as 
reported by man.  ls's last modified just isn't correct, at least on 
Ubuntu 20.04.2

Is this a quirk?  Am I doing something wrong?  Some kind of voodoo 
definition of "last modified"?  What does Linux say "last modified" 
really means?

FWIW, I am coming up to speed on processing these edf files to help out 
on an open source project.  Been working on some data analysis tools.  
As an aside, biological data is very messy.  It's been a treat to work 
on this as it's forced me to dust off the mental cobwebs and work on a 
problem that can help a lot of people.


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