L = [1, 2, 4, 8, 16, 32, 64]
X = 5

found = i = 0
while not found and i < len(L):
    if 2 ** X == L[i]:
        found = 1
    else:
        i = i+1

if found:
    print 'at index', i
else:
    print X, 'not found'


#-----------------------
# % python ex3_start.py
# at index 5
#-----------------------