获取python list的元素索引

1 python list 元素无重复，如下：

list_test = ["a", "b", "c", "d"]
a_index = list_test.index("a")
c_index = list_test.index("c")
print a_index
print c_index

# 结果：
  0
  2

1 python list 元素有重复，如下：

list_test = ["a", "b", "a", "c", "c", "d"]
for index, value in enumerate(list_test):
        print index, value

# 结果：
  0 a
  1 b
  2 a
  3 c
  4 c
  5 d