Python 推导式

推导式是Python语言的另一个特有特性，可以非常方便的从一个数据序列构建一个新的序列，支持列表、集合和字典的推导

1. 列表推导式

[]推导列表，()推导生成器

l = [i for i in range(10) if i % 4 == 0]
# l type is  <type 'list'>,  l value is  [0, 4, 8]
print 'l type is ', type(l), ', l value is ', l

g = (i for i in range(10) if i % 4 == 0)
# g type is  <type 'generator'> , g value is  <generator object <genexpr> at 0x100847320>
print 'g type is ', type(g), ', g value is ', g

2. 集合推导式

跟列表推导式的唯一区别是[]改为{}

l = {i for i in range(10) if i % 4 == 0}
# l type is  <type 'set'> , l value is  set([0, 8, 4])
print 'l type is ', type(l), ', l value is ', l

3. 字典推导式

d = {i: v for i, v in enumerate(range(2, 4)) if i == 0}
# d type is  <type 'dict'> , value is  {0: 2}
print 'd type is ', type(d), ', value is ', d