Python 推导式

1.列表(list)推导式

[out_exp_res for out_exp in input_list]
或者 
[out_exp_res for out_exp in input_list if condition]

names = ['Bob','Tom','alice','Jerry','Wendy','Smith']
new_names = [name.upper()for name in names if len(name)>3]
print(new_names)

输出：

['ALICE', 'JERRY', 'WENDY', 'SMITH']

2.字典(dict)推导式

{ key_expr: value_expr for value in collection }
或
{ key_expr: value_expr for value in collection if condition }

newdict = {key:len(key) for key in listdemo}
newdict

输出：

{'Google': 6, 'Runoob': 6, 'Taobao': 6}

3.集合(set)推导式

{ expression for item in Sequence }
或
{ expression for item in Sequence if conditional }

setnew = {i**2 for i in (1,2,3)}
setnew

输出：

{1, 4, 9}

4.元组(tuple)推导式（生成器表达式）  使用 tuple() 函数，可以直接将生成器对象转换成元组

(expression for item in Sequence )
或
(expression for item in Sequence if conditional )

a = (x for x in range(1,10))
tuple(a)      

输出：  返回a是一个生成器对象

(1, 2, 3, 4, 5, 6, 7, 8, 9)