By your requirement, you should iterate through all the values in L.
try out this code
P=3
I=2
L = [2,4,6,8,10]
x=[]
y=?
for i in L:
x.append((P * i * y)/I)
for idx,i in enumerate(x):
if x <= 305:
print "this" + L[idx] + "will not work"
else:
print "this" + L[idx] + "will not work"
solved For and If functions