A and B but not C in list

[Boris Borcic]

Terry Reedy wrote:
>
> The straightforward code
>
> if a in L and b in L and c not in L and d not in L
>
> scans the list 4 times.

of course for a single scan one can setify the list and write

S=set(L)
if a in S and b in S and c not in S and d not in S

or even, I guess, something like

{a,b} <= S and not S & {c,d}

also, I suppose that in some settings a,b,c,d could be made to belong to a class 
that has defined eg

__nonzero__ = __bool__ = S.__contains__

so that the if statement would become

if a and b and not c and not d

btw, did anybody ask the OP which if any of A,B,C,D otoh and L otoh would vary 
fastest ?

Whatever, BB