Launch file in Notepad

[George]

Newbie question:

I'm trying to lauch Notepad from Python to open a textfile:

import os
b1="c:\test.txt"
os.system('notepad.exe ' + b1)

However, the t of test is escaped by the \, resulting in Notepad trying 
to open "c: est.txt".

How do I solve this?

(By the way, b1 comes from a command line parameter, so the user enters 
c:\test.txt as command line parameter.)

George