> expr = [Or(s, Not(a) , Not(b)), Or(Not(s), Not(a), b), \
>             Or(Not(s), a, Not(b)), Or(s, a, b)]
> would be good

Do not use "\"! They can break too easily. Here it is not even
necessary since you are within a list statement. In general
I prefer to put a pair of "()" around the expressions to 
break instead of placing "\".