仅在右箭头后使字符串小写

Question

我想只在 Python 中的右箭头之后（直到它碰到逗号）将字符串变为小写。
另外，如果可以的话，我更喜欢用一行来写。
这是我的代码：

import re

line = "For example, →settle ACCOUNTs. After that, UPPER CASEs are OK."

string1 = re.sub(r'→([A-Za-z ]+)', r'→\1', line)
# string1 = re.sub(r'→([A-Za-z ]+)', r'→\1.lower()', line) # Pseudo-code in my brain
print(string1)
# Expecting: "For example, →settle accounts. After that, UPPERCASEs are OK."

# Should I always write two lines of code, like this:
string2 = re.findall(r'→([A-Za-z ]+)', line)
print('→' + string2[0].lower())
# ... and add "For example, " and ". After that, UPPER CASEs are OK." ... later?

我相信一定有更好的方法。你们会怎么做呢？
提前谢谢你。

Answer 1

import re

line = "For example, →settle ACCOUNTs. After that, UPPER CASEs are OK."

string1 = re.sub(r'→[A-Za-z ]+', lambda match: match.group().lower(), line)

print(string1)
# For example, →settle accounts. After that, UPPER CASEs are OK.

来自documentation：

re.sub(pattern, repl, string, count=0, flags=0)

...repl 可以是字符串或函数...

如果repl 是一个函数，则每次出现不重叠的模式都会调用它。该函数采用单个匹配对象参数，并返回替换字符串。