Sven的优秀代码做了一些多余的工作,可以使用元组解包而不是pop()。此外,它可以添加一个保护if x != y
来检查x和y是否不同。这是改进后的答案:
choices = {'a', 'b', 'c'}
x = 'a'
y = 'b'
if x != y:
z, = choices - {x, y}
这里有一个计时套件,用于展示相对性能的比较时间:
import timeit, itertools
setup_template = '''
x = %r
y = %r
choices = {'a', 'b', 'c'}
'''
new_version = '''
if x != y:
z, = choices - {x, y}
'''
original_version = '''
if x == 'a' and y == 'b' or x == 'b' and y == 'a':
z = 'c'
elif x == 'b' and y == 'c' or x == 'c' and y == 'b':
z = 'a'
elif x == 'a' and y == 'c' or x == 'c' and y == 'a':
z = 'b'
'''
for x, y in itertools.product('abc', repeat=2):
print '\nTesting with x=%r and y=%r' % (x, y)
setup = setup_template % (x, y)
for stmt, name in zip([original_version, new_version], ['if', 'set']):
print min(timeit.Timer(stmt, setup).repeat(7, 100000)),
print '\t%s_version' % name
以下是时间结果:
Testing with x='a' and y='a'
0.0410830974579 original_version
0.00535297393799 new_version
Testing with x='a' and y='b'
0.0112571716309 original_version
0.0524711608887 new_version
Testing with x='a' and y='c'
0.0383319854736 original_version
0.048309803009 new_version
Testing with x='b' and y='a'
0.0175108909607 original_version
0.0508949756622 new_version
Testing with x='b' and y='b'
0.0386209487915 original_version
0.00529098510742 new_version
Testing with x='b' and y='c'
0.0259420871735 original_version
0.0472128391266 new_version
Testing with x='c' and y='a'
0.0423510074615 original_version
0.0481910705566 new_version
Testing with x='c' and y='b'
0.0295209884644 original_version
0.0478219985962 new_version
Testing with x='c' and y='c'
0.0383579730988 original_version
0.00530385971069 new_version
这些时间表明,原始版本的性能会根据各种输入值触发的if语句而有所不同。