我有一个包含 9 个元素的列表。前三个代表位置,下一个速度,下一个力。
有时我需要来自阵列的力,有时需要速度,有时需要位置。
于是我写了一个函数如下:
def Extractor(alist,quantity):
if quantity=='positions':
x = alist[0]
y = alist[1]
z = alist[2]
return (x,y,z)
elif quantity=='velocities':
vx = alist[3]
vy = alist[4]
vz = alist[5]
tot_v = np.sqrt(vx**2 + vy**2 + vz**2)
return (vx,vy,vz,tot_v)
elif quantity=='forces':
fx = alist[6]
fy = alist[7]
fz = alist[8]
tot_f = np.sqrt(fx**2 + fy**2 + fz**2)
return (fx,fy,fz,tot_f)
else:
print "Do not recognise quantity: not one of positions, velocities, force"
但是,由于代码重复,这对我来说似乎是一种巨大的代码味道。有没有更好、更 pythonic 的方法来做到这一点?我对 OOP 很陌生,但我可以使用某种利用多态性的类继承吗?
最佳答案
您的方法违反了 Single Responsibility Principle .考虑像这样拆分它:
def positionExtractor(alist):
return tuple(alist[0:3])
def velocityExtractor(alist):
velocity = tuple(alist[3:6])
return velocity + (np.sqrt(sum(x**2 for x in velocity)),)
def forcesExtractor(alist):
forces = tuple(alist[6:9])
return forces + (np.sqrt(sum(x**2 for x in forces)),)
你可以把它们放在字典里:
extractors = {
'position' : positionExtractor,
'velocity' : velocityExtractor,
'forces' : forcesExtractor}
并使用:
result = extractors[quantity](alist)
这是一个继承的例子。不过,对于这样一个简单的任务来说,它似乎是过度设计的:
import numpy as np
class Extractor:
def extract(self, alist):
raise NotImplementedError()
class IndexRangeExtractor(Extractor):
def __init__(self, fromIndex, toIndex):
self.fromIndex = fromIndex
self.toIndex = toIndex
def extract(self, alist):
return tuple(alist[self.fromIndex:self.toIndex])
class EuclideanDistanceExtractorDecorator(Extractor):
def __init__(self, innerExtractor):
self.innerExtractor = innerExtractor
def extract(self, alist):
innerResult = self.innerExtractor.extract(alist)
distance = np.sqrt(sum(x**2 for x in innerResult))
return innerResult + (distance,)
#...
class ExtractorFactory:
def __init__(self):
self.extractors = {
'position':IndexRangeExtractor(0, 3),
'velocity':EuclideanDistanceExtractorDecorator(
IndexRangeExtractor(3, 6)),
'forces':EuclideanDistanceExtractorDecorator(
IndexRangeExtractor(6, 9))}
def createExtractor(self, quantity):
return self.extractors[quantity]
alist = [1,2,3,4,5,6,7,8,9]
ef = ExtractorFactory()
e1 = ef.createExtractor('position')
e2 = ef.createExtractor('velocity')
e3 = ef.createExtractor('forces')
print e1.extract(alist)
print e2.extract(alist)
print e3.extract(alist)
关于python - 代码味道 - if/else 构造,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/20497748/