我有一个字符串和一个数字。我需要找到包含与数字长度相同的字符的第一个子字符串

def find_substring(string, number):
    number_str = str(number)
    number_length = len(number_str)
    
    for i in range(len(string) - number_length + 1):
        substring = string[i:i+number_length]
        if substring == number_str:
            return substring
    
    return None

# 示例用法
string = "I have a string and a number. I need to find the first substring that contains characters of the same length as the number."
number = 12345

result = find_substring(string, number)
print(result)