Python base64混淆报错：expected str instance, bytes found

问题描述 #

我在个人项目中尝试对Base64字符串做混淆处理：每间隔指定长度的字符插入多个@符号，再通过Base64 UTF-8编码，重复该流程多次。作为Python新手，参考他人代码修改后适配需求，但不确定语法正确性。当前使用Python 3.10.5 64位版本，在VSCode运行代码时出现TypeError: sequence item 0: expected str instance, bytes found错误，相关代码及完整报错信息如下：

import base64
# Define 'encrypt' function to append @ signs. This could ostensibly be changed to any character that is not part of the base64 character set.
def encrypt(string, length):
    return '@@@@'.join(string[i:i+length] for i in range(0,len(string),length))

# Get user input
encString = input("Enter string to obfuscate:")
print("Enter Integer:")
loops = input()

# Set loops as an int as I was having problems with it being defined as a string, attempted to do the same for encString
x = int(loops)
encString = str(encString)

# Attempt to loop this for the specified number of times
while x != 0:
    x = x - 1
    encString = encrypt(encString,4)
    encString = base64.b64encode (bytes(encString, "utf-8"))

print(encString)

报错信息：

PS C:\Users\esmith> & C:/Users/esmith/AppData/Local/Programs/Python/Python310/python.exe "c:/Users/esmith/PATH/Documents/Learning Python/test.py"
Enter string to obfuscate:bnVtYmVyID0gMSArIDIgKiAzIC8gNApwcmludChudW1iZXIpCgpyZW1haW5kZXIgPSAxMSAlIDMKcHJpbnQocmVtYWluZGVyKQoKIyBUd28gKiogMgpjdWJlZCA9IDIgKiogMwpwcmludChzcXVhcmVkKQpwcmludChjdWJlZCkKCmxvdHNvZmhlbGxvcyA9ICJoZWxsbyAiICogMTAKcHJpbnQobG90c29maGVsbG9zKQoKCmV2ZW5fbnVtYmVycyA9IFsyLDQsNiw4XQpvZGRfbnVtYmVycyA9IFsxLDMsNSw3XQphbGxfbnVtYmVycyA9IG9kZF9udW1iZXJzICsgZXZlbl9udW1iZXJzCnByaW50KGFsbF9udW1iZXJzKQoKCnByaW50KFsxLDIsM10gKiAzKQ==
Enter Integer:
5
Traceback (most recent call last):
  File "c:\Users\esmith\PATH\Documents\Learning Python\test.py", line 15, in <module>
    encString = encrypt(encString,4)
  File "c:\Users\esmith\PATH\Documents\Learning Python\test.py", line 4, in encrypt
    return '@@@@'.join(string[i:i+length] for i in range(0,len(string),length))
TypeError: sequence item 0: expected str instance, bytes found

错误原因 #

核心问题是数据类型不匹配：

• base64.b64encode()函数返回的是bytes类型对象，而非字符串
• 第一次循环时，encString是字符串，encrypt()可以正常处理；但经过base64.b64encode()处理后，encString变成了bytes对象
• 第二次循环调用encrypt()时，string[i:i+length]取到的是bytes片段，而'@@@@'.join()要求所有元素必须是字符串类型，因此触发类型错误

解决方法 #

每次调用base64.b64encode()后，必须将返回的bytes对象解码为UTF-8字符串，确保后续循环中encString始终保持字符串类型，避免类型冲突。

修正后的代码 #

import base64

def encrypt(string, length):
    return '@@@@'.join(string[i:i+length] for i in range(0, len(string), length))

encString = input("Enter string to obfuscate:")
print("Enter Integer:")
loops = input()

x = int(loops)
encString = str(encString)

while x != 0:
    x = x - 1
    encString = encrypt(encString, 4)
    # 关键修改：对b64encode的返回值进行utf-8解码，转为字符串
    encString = base64.b64encode(bytes(encString, "utf-8")).decode("utf-8")

print(encString)

验证说明 #

修正后，每次循环结束后encString都会保持字符串类型，encrypt()函数可正常处理，不会再触发类型错误，可输入测试值验证混淆流程是否符合预期。

内容的提问来源于stack exchange，提问作者Eben Smith