这个情况应该怎么办呢？
TypeError: sequence item 0: expected str instance, bytes found

代码def recvall(sock,length):
blocks=[]
while length:
block=sock.recv(length)
if not block:
raise EOFError('socket closed with %d bytes left'
'in this block'.format(length))
length -=len(block)
blocks.append(block)
return ''.join(blocks)

def get_block(sock):
data=recvall (sock,header_struct.size)
(block_length,)=header_struct.unpack(data)
return recvall(sock,block_length)

def put_block(sock,message):
block_length=len(message)
sock.send(header_struct.pack(block_length))
sock.send(message)
其中def get_block(sock)中第三行的data 老报错