python中，遍歷dict的方法有四種。但這四種遍歷的效能如何呢？我做了如下的測試

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=clock()

for k,v in zip(d.iterkeys(),d.itervalues()):
    t = k + v
t4=clock()

print t1-t0, t2-t1, t3-t2, t4-t3 
 

python test.py
0.00184039735833 0.00326492977712 0.00214993552657 0.00311549755797

python test.py
0.00182356570728 0.00339342506446 0.00234863111466 0.00321566640817

python test.py
0.00185107108827 0.00324563495762 0.00211175641563 0.00313479237748

python test.py
0.0018215130669 0.00320950848705 0.00215814608806 0.00322798225041

python test.py
0.00216635664955 0.00391807994377 0.00207604047314 0.00322757172233
 

不過實際的差別不是太大，不必過於糾結