通过扩展创建缓冲区类的Python海峡

Question

我想这是最好的代码和注释说明：

import struct 

class binary_buffer(str): 
    def __init__(self, msg=""): 
     self = msg 
    def write_ubyte(self, ubyte): 
     self += struct.pack("=B", ubyte) 
     return len(self) 

Output 
>> bb = binary_buffer() 
>> bb # Buffer starts out empty, as it should 
'' 
>> bb.write_ubyte(200) 
1 # We can see that we've successfully written one byte to the buffer 
>> bb 
'' # Huh? We just wrote something, but where has it gone? 

Answer 1

str s为不可变的。因此，

self += struct.pack("=B", ubyte) 

被评估为

self = self + struct.pack("=B", ubyte) 

此赋新值的名称自我，而是自我，就像任何其他的名称。一旦方法退出，名称（和关联的对象）就会被忘记。

你想要一个bytearray：

>>> bb = bytearray() 
>>> bb.append(200) 
>>> bb 
bytearray(b'\xc8')