Python 中的 `swapcase()` 函数有助于返回原始字符串的副本，其中字符串中所有大写字符都转换为小写，所有小写字符都转换为大写。
string.swapcase()
`swapcase()` 方法不接受任何参数。如果我们调用此函数，所有大小写（大写和小写）都将被反转。
返回值始终是字符串。转换时，所有符号和字母都将被忽略。
| 输入 | 返回值 |
|---|---|
| 字符串 | 大小写转换后的字符串 |
# example string
string1 = "CONVERTING INTO LOWERCASE."
print(string1.swapcase())
string2 = "converting into uppercase."
print(string2.swapcase())
string3 = "String Have Both Upper And Lowercase."
print(string3.swapcase())
输出
converting into lowercase. CONVERTING INTO UPPERCASE. sTRING hAVE bOTH uPPER aND lOWERCASE.
string = "HI HOW ARE YOU?"
print(string.swapcase())
string = " I am fine."
print(string.uppercase())
输出
hi how are you? IAM FINE.
