Help sorting a list by file extension

[Peter A. Schott]

Trying to operate on a list of files similar to this:

test.1
test.2
test.3
test.4
test.10
test.15
test.20

etc.

I want to sort them in numeric order instead of string order.  I'm starting with
this code:

import os

for filename in [filename for filename in os.listdir(os.getcwd())]:
	print filename
	#Write to file, but with filenames sorted by extension


Desired result is a file containing something like:
C:\MyFolder\test.1,test.001
C:\MyFolder\test.2,test.002
C:\MyFolder\test.3,test.003
C:\MyFolder\test.4,test.004
C:\MyFolder\test.10,test.010
C:\MyFolder\test.15,test.015
C:\MyFolder\test.20,test.020

I need to order by that extension for the file output.

I know I've got to be missing something pretty simple, but am not sure what.
Does anyone have any ideas on what I'm missing?

Thanks.

-Pete Schott