python中，遍历dict的方法有四种。但这四种遍历的性能如何呢？我做了如下的测试 l = [(x,x) for x in xrange(10000)] d = dict(l) from time import clock t0=clock() for i in d: t = i + d[i] t1=clock() for k,v in d.items(): t = k + v t2=clock() for k,v in d.iteritems(): t = k + v t3=cloc