python 列表推导

1.

numbers = range(10)
size = len(numbers)
evens = []
i = 0
while i < size:
    if i % 3 == 0:
        evens.append(i)
    i += 1
    
print(evens)

以上是痛苦的，在c语言中或许可行，在python中却是不合理的，执行速度会很慢。

简化为：

 

[i for i in range(10) if i % 3 == 0]

 

2.

i = 0
seq = ["one","two","three"]
for element in seq:
    seq[i] = '%d: %s'%(i,seq[i])
    i += 1
print(seq)

简化为：
 

seq = ["one","tewo","three"]
for i,element in enumerate(seq):
    seq[i] = '%d: %s'%(i,seq[i])

print(seq)

重构：
 

def reement(pos,element):
    print('%d:%s'% (pos,element))
    
seq = ["one","two","three"]

[reement(i,el) for i,el in enumerate(seq)]