python 基础(六) 推导式

列表推导式

概念：提供了一种创建列表的简单快速的途径

(1) 一般形式

myList = [x for x in range(10)]

​

#分解后

myList = []

for x in range(10):

    myList.append(x)

print(myList)

(2) 一般形式+判断

myList = [x for x in range(1,21) if x>10]

myList = [x for x in range(1,21) if x%2==0 and x<10]

(3) 生成列表嵌套

#第三种 生成列表嵌套

myList = [[x,x+1,x+2] for x in range(10)]

print(myList)

(4) 循环嵌套

#第四种 循环嵌套

myList = [x for x in range(3) for y in range(10)]

myList = [[x,y] for x in range(3) for y in range(10)]

3*4矩阵列表

myList = [

    [1,2,3,4],

    [5,6,7,8],

    [9,10,11,12]

]

变成4*3矩阵列表

newList = [[v[i] for v in myList] for i in range(4)]

拆分

newList = []

for i in range(4):

    appendList = []

    for v in myList:

        # print(v[i])

        appendList.append(v[i])

    newList.append(appendList)

print(newList)

(5) 字典推导式

Dict = {k:v for k,v in [('a','a'),('b','b')]}

print(Dict)