>I don't understand what you mean when you say "how umask works in 
>relation to Python".  How it works in relation to Python isn't different 
>from how it works for any other Unix program.  Consider, for example, 
>the unix man page for 'open'.

This is what I mean.
The following gnu commands give (on Archlinux):
$ umask
0022
$ mkdir test1
$ mkdir test2 --mode 0777
$ ls -l
drwxr-xr-x 2 sindrero users 4096 Jun 15 00:59 test
drwxrwxrwx 2 sindrero users 4096 Jun 15 00:59 test2

So we see that new folder created with the --mode parameter to gnu's mkdir does not get the umask masked out.

The following code in python gives:
>> import os
>> os.mkdir('test3')
>> os.mkdir('test4')
>> exit()
$ ls -l
drwxr-xr-x 2 sindrero users 4096 Jun 15 01:01 test3
drwxr-xr-x 2 sindrero users 4096 Jun 15 01:01 test4

I (as a programmer) have never seen the specific code for python's mkdir function, And I have no way to know whether I should presume that mkdir in python works the same way as the gnu command or not. Unless it is documented that is.

Cheers :)