1. lower()
python自带解释：
| lower(...)
| S.lower() -> str
|
| Return a copy of the string S converted to lowercase.
举个栗子：
>>>s = 'Hello World!'
>>>print(s.lower())
hello world!
2. upper()
python自带解释：
| upper(...)
| S.upper() -> str
|
| Return a copy of S converted to uppercase.
举个栗子：
>>>s = 'Hello World!'
>>>print(s.upper())
HELLO WORLD!
3. swapcase()
python自带解释：
| swapcase(...)
| S.swapcase() -> str
|
| Return a copy of S with uppercase characters converted to lowercase
| and vice versa.
举个栗子：
>>>s = 'Hello World!'
>>>print(s.swapcase())
hELLO wORLD!
4. title()
python自带解释：
title(...)
| S.title() -> str
|
| Return a titlecased version of S, i.e. words start with title case
| characters, all remaining cased characters have lower case.
举个栗子：
>>>s = 'I love you!'
>>>print(s.title())
I Love You!
5. capitalize()
python自带解释：
| capitalize(...)
| S.capitalize() -> str
|
| Return a capitalized version of S, i.e. make the first character
| have upper case and the rest lower case.
举个栗子：
>>>s1 = 'Hello World!'
>>>s2 = 'I love you!'
>>>print(s1.capitalize())
Hello world!
>>>pirnt(s2.capitalize())
I love you!
总结
输入
s = 'I love you!'
print(s.upper())
print(s.lower())
print(s.capitalize())
print(s.swapcase())
print(s.title())
输出
I LOVE YOU!
i love you!
I love you!
i LOVE YOU!
I Love You!
