代码…

options.get(something, doThisMostOfTheTime)()

…看起来它应该更快，但它实际上比if … elif … else构造，因为它必须调用一个函数，这可能是一个严重的性能开销在一个紧的循环。

考虑这些例子…

1.py

something = 'something'

for i in xrange(1000000):

if something == 'this':

the_thing = 1

elif something == 'that':

the_thing = 2

elif something == 'there':

the_thing = 3

else:

the_thing = 4

2.py

something = 'something'

options = {'this': 1, 'that': 2, 'there': 3}

for i in xrange(1000000):

the_thing = options.get(something, 4)

3.py

something = 'something'

options = {'this': 1, 'that': 2, 'there': 3}

for i in xrange(1000000):

if something in options:

the_thing = options[something]

else:

the_thing = 4

4.py

from collections import defaultdict

something = 'something'

options = defaultdict(lambda: 4, {'this': 1, 'that': 2, 'there': 3})

for i in xrange(1000000):

the_thing = options[something]

…并记下它们使用的CPU时间量…

1.py: 160ms

2.py: 170ms

3.py: 110ms

4.py: 100ms

…使用用户时间从time(1)。

选项#4确实有额外的内存开销，为每个不同的密钥未命中添加一个新的项目，所以如果你期望无限多个不同的密钥未命中，我会选择#3，这仍然是一个重大的改进原始结构。