Python ljust rjust center输出

看下面的例子就会明白了：

print '|','*'.ljust(10),'|' 
print '|','*'.ljust(10,'-'),'|' 
print '|','*'.rjust(10,'-'),'|' 
print '|','*'.center(10,'-'),'|' 
for a in range(1, 6): 
print 'a = '.ljust(5), repr(a).ljust(10), 'b = '.ljust(5), repr(a * 2)

输出结果:
| * |
| *--------- |
| ---------* |
| ----*----- |
a = 1 b = 2
a = 2 b = 4
a = 3 b = 6
a = 4 b = 8
a = 5 b = 10