array = [1,2,3,4,5,6]small = []for n in array:if n <4: small.append(n *2)print(small)# [2,4,6]
比较地道的 python 写法是使用列表推导:
array = [1,2,3,4,5,6]small = [n *2for n in array if n <4]
for in 可以写两次,类似于嵌套的 for 循环,会得到一个笛卡尔积:
signs = ['+','-']numbers = [1,2]ascii= ['{sign}{number}'.format(sign=sign, number=number)for sign in signs for number in numbers]# 得到:[‘+1’, ‘+2’, ‘-1’, ‘-2’]