按大小顺序打印给定字符串的所有子字符串

def print_substrings(string):
    substrings = []
    length = len(string)
    
    for i in range(length):
        for j in range(i+1, length+1):
            substring = string[i:j]
            substrings.append(substring)
    
    substrings.sort(key=len)  # 按照子字符串的大小顺序排列
    
    for substring in substrings:
        print(substring)

# 测试示例
string = "abcd"
print_substrings(string)

a
b
c
d
ab
bc
cd
abc
bcd
abcd