Use of strings in python code

I don't understand why the robot does not move when I add a string variable. For example:

import thymio

var1 ="B"
thymio.leftwheel.setpower(100)
thymio.rightwheel.setpower(100)
while True:
if var1 == "B":
thymio.leftwheel.setpower(100)
thymio.rightwheel.setpower(0)
else:
thymio.leftwheel.setpower(0)
thymio.rightwheel.setpower(100)

The robot does not drive at all when using this code.

Ah the indentation is removed when posted the reply, so assume that the identation was correct :-)