Python 迭代dict 效率

import timeit

DICT_SIZE = 100 * 100000

testDict = dict()
for i in xrange(DICT_SIZE):
    testDict[i] = i

assert len(testDict) == DICT_SIZE

def test1():
    for _ in testDict.keys():
        pass

def test2():
    for _ in testDict.iterkeys():
        pass

def test3():
    for _ in testDict:
        pass

print timeit.timeit("test1()", setup="from __main__ import test1", number=2000)
print timeit.timeit("test2()", setup="from __main__ import test2", number=2000)
print timeit.timeit("test3()", setup="from __main__ import test3", number=2000)

4198.55953097
1695.41651607
1896.270154