upper()字符串中字母由小写变为大写
lower()字符串中字母由大写变为小写
capitalize()字符串中字母首字母大写其余小写
title()字符串中字母每个单词的首字母大写其余小写
举个列子：
1 a = "hello" 2 b = "WORLD" 3 c = "hello" 4 d = "hello world" 5 a1 = a.upper() 6 b1 = b.lower() 7 c1 = c.capitalize() 8 d1 = d.title() 9 print(a1) 10 print(b1) 11 print(c1) 12 print(d1)
输出结果：
HELLO
world
Hello
Hello World
实际运用就如上面代码书写。