class Solution:
# @param {string} s
# @return {string[]}
def findRepeatedDnaSequences(self, s):
dic = {}
for i in xrange(len(s)9):
dic[s[i:i+10]] = dic.get(s[i:i+10], 0) + 1
return [res for res in dic.keys() if dic[res]>1]
Possible the shortest Python code?

Not bad, but here's a shorter one:
class Solution: def findRepeatedDnaSequences(self, s): d = {}, {} for i in range(len(s)9): d[s[i:i+10] in d[0]][s[i:i+10]] = 1 return list(d[1])
Although I rewrote it like that just for comparison/shortness. Originally it looked like this:
class Solution: def findRepeatedDnaSequences(self, s): once, twice = set(), set() for i in range(len(s)  9): ss = s[i:i+10] [once, twice][ss in once].add(ss) return list(twice)