# 从特定键开始迭代排序的字典项

NI6

OrderedDict用来存储一些项目，如下所示：

d = OrderedDict(zip(['a', 'b', 'c', 'd'], range(4)))

d等于{'a': 0, 'b': 1, 'c': 2, 'd': 3}

from __future__ import print_function

from collections import OrderedDict
from itertools import dropwhile

d = OrderedDict(zip(['a', 'b', 'c', 'd'], range(4)))

for k, v in dropwhile(lambda x: x[0] != 'b', d.items()):
print(k, v)

b 1
c 2
d 3

Python 2，避免使用.items()::创建键值列表

for k, v in dropwhile(lambda x: x[0] != 'b', d.iteritems()):
print(k, v)

### 定时

%timeit
for each in d.items()[d.keys().index('b'):]:
pass
The slowest run took 5.18 times longer than the fastest. This could mean that an intermediate result is being cached.
100000 loops, best of 3: 3.27 µs per loop

%%timeit
for each in islice(d.iteritems(), d.keys().index('b'), None):
pass
The slowest run took 5.23 times longer than the fastest. This could mean that an intermediate result is being cached.
100000 loops, best of 3: 3.05 µs per loop

%%timeit
for k, v in dropwhile(lambda x: x[0] != 'b', d.iteritems()):
pass
The slowest run took 4.92 times longer than the fastest. This could mean that an intermediate result is being cached.
100000 loops, best of 3: 2.23 µs per loop

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