迭代dict也要讲求效率，不然就要走进性能陷阱
以下三种迭代方式：keys，iterkeys, hashkey
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)
结果：
4198.55953097
1695.41651607
1896.270154
keys()会生成一个list，耗内存又耗时间；iterkeys是迭代key，不会生成list。第二和第三方法相差不多。