从存在和不存在搜索字符串的字符串中检索特定文本

def retrieve_text(target_string, search_string):
    if search_string in target_string:
        start_index = target_string.find(search_string)
        end_index = start_index + len(search_string)
        retrieved_text = target_string[start_index:end_index]
        return retrieved_text
    else:
        return "Search string not found in target string."

# 示例用法
target_string = "This is a sample string."
search_string = "sample"
result = retrieve_text(target_string, search_string)
print(result)  # 输出：sample

search_string = "notfound"
result = retrieve_text(target_string, search_string)
print(result)  # 输出：Search string not found in target string.