Python format string, placeholders, merge array

Array merge

Reference link: https: //www.cnblogs.com/chaihy/p/7243143.html

>>> a=[2]
>>> b=[3]
>>> a.extend(b)
>>> a
[2, 3]
>>>

　　

Placeholder

　　Reference link: https: //www.cnblogs.com/lvcm/p/8859225.html

　　Correct usage of placeholders

A = 2 >>> 
>>> Print ( '% S SS'% A) without intermediate comma # 
ss2