[Tutor] Sorting specific files by modification date

[Fiyawerx]

I'm working on a small script that so far, using the xlrd module, (
http://www.lexicon.net/sjmachin/xlrd.html) will parse all the files in a
given directory for a xls file with a specific worksheet. This way, if the
file names change, or people don't save the spreadsheet with the right name,
my script will still be able to locate the correct files to use for it's
data source out of multiple files / versions. So far what I have sort of
goes like this :

import os
import xlrd

data = {}

#path may be set externally at some point
data['path'] = 'mypath_to_program'

os.chdir(data['path'])

data['xls_files'] = [ file for file in os.listdir('./') if '.xls' in file ]

first_files = [ file for file in data['xls_files'] if u'First Worksheet' in
xlrd.open_workbook(file).sheet_names() ]
data['first_file'] = ??

second_files = [ file for file in data['xls_files'] if u'Second Worsheet' in
xlrd.open_workbook(file).sheet_names() ]
data['second_file'] = ??

This is where I get stuck, I'm trying to figure out how, from the files that
match, I can select the file with the most current time stamp and use that
as my main data file.
I know I can get the modification time with os.stat(file).st_mtime, but I'm
not sure how I can sort my returns by this, to get just the most current
version. Any help / thoughts would be appreciated. I'm going to be looking
for other worksheets as well that might be in other xls's, for example
'Second Worksheet' also, but I was just trying to get the 'first_files'
working first. Instead of opening them each time, should I construct some
type of data that stores the file, it's worksheets, and its modification
times for each file found, and then just parse that list? like maybe change
my xls_files around to not just be a list of names?
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