（1）< （默认）左对齐、> 右对齐、^ 中间对齐、= （只用于数字）在小数点后进行补齐
（2）取位数“{:4s}”、"{:.2f}"等
1 >>> print('{} and {}'.format('hello','world')) # 默认左对齐
2 hello and world
3 >>> print('{:10s} and {:>10s}'.format('hello','world')) # 取10位左对齐，取10位右对齐
4 hello and world
5 >>> print('{:^10s} and {:^10s}'.format('hello','world')) # 取10位中间对齐
6 hello and world
7 >>> print('{} is {:.2f}'.format(1.123,1.123)) # 取2位小数
8 1.123 is 1.12
9 >>> print('{0} is {0:>10.2f}'.format(1.123)) # 取2位小数，右对齐，取10位
10 1.123 is 1.12