重複取り出し

setを使うべきでした。

#!/usr/bin/env python
#-*- coding:utf-8 -*-

answer0 = 'a'
answer1 = 'b'
answer2 = 'c'
answer3 = 'b'
answer4 = 'd'

passPhrases = (answer0, answer1, answer2, answer3, answer4, )
sets = set('')
ret = []
size = 0
for item in passPhrases:
    sets.add(item)
    if len(sets)== size:
        ret.append(item)

    size = len(sets)

print ret
dups = {}
for dup in ret:
    duplist = []
    pos =0
    for item in passPhrases:
        if item == dup:
            duplist.append(pos)
        pos =pos + 1

    dups[dup] = duplist

print dups