binary search

import sys

s = raw_input('give a string: ')
n = len(s)
low = 0
high = n-1
ans = (high-low)/2

x = ()
l = ''

print "Give a letter: "
l = sys.stdin.read(1)

if n != 0:
    if l != s[0] and l != s[n-1]:
        if l == s[ans]:
            a = 0
            b = 1
            while l == s[ans-a]:
                x = x + (ans-a,)
                a += 1
            while l == s[ans+b]:
                x = x + (ans+b,)
                b += 1
        else:
            while l != s[ans]:
                if s[ans] > l:
                    high = ans
                else:
                    low = ans
                ans = (high + low)/2

                if low == ans or high == ans:
                    break

            a = 0
            b = 1
            while l == s[ans-a]:
                x = x + (ans-a,)
                a += 1
            while l == s[ans+b]:
                x = x + (ans+b,)
                b += 1

    if l == s[0]:
        a = 0
        while l == s[a]:
            x = x + (a,)
            a += 1
            if a >= n:
                break

    if l == s[n-1] and l != s[0]:
        b = 1
        while l == s[n-b]:
            x = x + (n-b,)
            b += 1

if x == ():
    print 'Er zit geen %s in de gegenven string!' % l
else:
    print "%s" % (x,)