如何在不使用拆分、子字符串或索引的情况下在某个字符上剪切字符串？

import re

def cut_string(string, character):
    pattern = f"{character}.*"
    result = re.sub(pattern, "", string)
    return result

def keep_string(string, character):
    pattern = f".*{character}"
    result = re.sub(pattern, "", string)
    return result

# 示例用法
string = "example@example.com"
character = "@"

cut_result = cut_string(string, character)
print("剪切后的字符串：", cut_result)

keep_result = keep_string(string, character)
print("保留的字符串：", keep_result)

剪切后的字符串： example
保留的字符串： example@