python将list中的每一个str型元素转换为int型元素（一维和二维）

例如 a=["1","2","3","4"]想要转换为 a=[1,2,3,4],有以下两种方法

方法一：列表推导式

a = [int(num) for num in a]

方法二：map()

a = list(map(int,a))

针对二维列表

a=[["1","2","3","4"],["4","5","6","7"]]

a = [[ int(num) for num in lst ] for lst in a]