本篇Cookbook的小技巧很有用处，一言难尽，请看示例代码：

numbers = [1,2,3,4,5]
s=sum(x*x for x in numbers if x > 3)
print(s)

l=list(2*x for x in numbers if x % 2 == 0)
print(l)

大家应该可以通过上面的例子体会到Python的简洁与优雅。

借孟哥的代码，我也扩充下，

numbers = [x for x in range(1,6)]
s=sum(x*x for x in numbers if x > 3 and x % 2 == 0)
print(s)
 
l=list(2*x for x in numbers if x % 2 == 0 or x % 2 != 0 )
print(l)

我感觉 列表推导式是python的金典  

a = {'x' : 1,'y' : 2,'z' : 3}     b = {'w' : 10,'x' : 11,'y' : 2}

c = {key:a[key] for key in a.keys() - {'z', 'w'}}

看了楼上的，想到了在字典上的应用

a = [['a1',1],['a2',2]]

b = dict(x for x in a)