如何在python 3中找到某个文本前的字符串的子串最短

def find_shortest_substring(text, target):
    index = text.find(target)  # 查找目标子串的索引位置
    if index == -1:
        return None  # 如果找不到目标子串，则返回None

    substring = text[:index]  # 获取目标子串之前的子串
    shortest_substring = min(substring.split(), key=len)  # 使用空格分割子串，并找到最短的子串

    return shortest_substring

text = "This is a sample text. This is another sample text."
target = "sample"
result = find_shortest_substring(text, target)
print("最短的子串是:", result)

最短的子串是: a