assigning index

[3Pinter]

Basicly I have a certain amount of positions (1-3) which can be either True or False.

I want the function I use to get the decent index value.

So
pos1 T
pos2 F
pos3 T
gives indexes 0 and 1

while example below gives 0, 1, 2

and
pos1 T
pos2 F
pos3 F
gives index 0

To me my code feels a bit strange. Lack of knowledge for sure, so what would you suggest?

triggers = [100,200,300]

pos1 = True #never changes
pos2 = True
pos3 = True

Somevalue = 3

pos1 = triggers[0]
if pos2:
    customfunction(a, b, triggers[1])
    if pos3:
        customfunction(a, c,triggers[2])
elif pos3:
	customfunction(a, c, triggers[1])