python 的 socket.recv 的返回值的疑问（用 markdown 重写了一次主题）

#socket 的 API 文档

socket.recv(bufsize[, flags])

Receive data from the socket. The return value is a string representing the data received. The maximum amount of data to be received at once is specified by bufsize. See the Unix manual page recv(2) for the meaning of the optional argument flags; it defaults to zero.

这里说 return value is a string representing 是什么意思？如下的程序，客户端为什么 print data 打印出的是乱码，这个不是 ASCII 码表示的 510 吗？

-------------------------------------客户端-------------------------

# Echo server program
import socket

HOST = ''                 # Symbolic name meaning all available interfaces
PORT = 50007              # Arbitrary non-privileged port
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
s.listen(1)
conn, addr = s.accept()
print 'Connected by', addr
while 1:
    data = conn.recv(1024)
    if not data: break
    conn.sendall(data)
conn.close()

---------------------------------服务器端--------------------------------------

# Echo client program
import socket

HOST = '127.0.0.1'    # The remote host
PORT = 50007              # The same port as used by the server
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.sendall('\x05\x01\x00')
data = s.recv(1024)
s.close()

print data
print 'Received', repr(data)