Python学习二

er = [[1,2,3],
      [4,5,6],
      [7,8,9]] 
print(er)#此处有一处莫名奇妙的错误，如果print(er)这条语句前面有空格的话，
        #则会报错"unexpected indent",若去掉空格则运行成功
        #暂时还不了解python的运行机制
cols = [row[1] for row in er]
        #解释一下“row[1] for row in er” 的意思
        #row[1] 为第1行 应为在er这个数组里面的一行
print(cols)
cols = [row[1]+1 for row in er]
print(cols) 
num1 = 10
cols = [row[1]-num1 for row in er]
print(cols)
cols = [row[1]+1 for row in er if row[1]%2==0 ]
print(cols)
cols = [er[i][i] for i in [0,1,2]]
print(cols)