问题是:client() 中的 print() 只输出一行，而我希望它打印多行，因为 while 它所在的循环显然运行了不止一次。

当我测试Foundations of Python Network Programming, 3rd Edition一书中给出的示例代码时出现问题。此示例代码基本上创建了一个简单的 TCP 服务器/客户端，用于处理/发送简单的文本大写请求。以下是代码:

#!/usr/bin/env python3
# Foundations of Python Network Programming, Third Edition
# https://github.com/brandon-rhodes/fopnp/blob/m/py3/chapter03/tcp_deadlock.py
# TCP client and server that leave too much data waiting
import argparse, socket, sys

def server(host, port, bytecount):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.bind((host, port))
    sock.listen(1)
    print('Listening at', sock.getsockname())
    while True:
        sc, sockname = sock.accept()
        print('Processing up to 1024 bytes at a time from', sockname)
        n = 0
        while True:
            data = sc.recv(1024)
            if not data:
                break
            output = data.decode('ascii').upper().encode('ascii')
            sc.sendall(output) # send it back uppercase
            n += len(data)
            print('\r %d bytes processed so far' % (n,), end=' ')
            sys.stdout.flush()
        print()
        sc.close()
        print('  Socket closed')

def client(host, port, bytecount):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    bytecount = (bytecount + 15) // 15 * 16 # round up to a multiple of 16
    message = b'CAP!' # 16-byte message to repeat over and over

    print('Sending', bytecount, 'bytes of data, in chunks of 16 bytes')
    sock.connect((host, port))
    sent = 0
    while sent < bytecount:
        sock.sendall(message)
        sent += len(message)
        # print('test')
        print('\r %d bytes sent' %(sent,), end=' ') # <-- THIS IS THE PROBLEMATIC PRINT()
        sys.stdout.flush()

    print()
    sock.shutdown(socket.SHUT_WR)

    print('Receiving all the data the server sends back')

    received = 0
    while True:
        data = sock.recv(42)
        if not received:
            print('  The first data received says', repr(data))
        if not data:
            break
        received += len(data)
        print('\r %d bytes received' %(received,), end=' ')

    print()
    sock.close()

if __name__ == '__main__':
    choices = {'client': client, 'server': server}
    parser = argparse.ArgumentParser(description='Get deadlocked over TCP')
    parser.add_argument('role', choices=choices, help='which role to play')
    parser.add_argument('host', help='interface the server listens at;'
                        ' host the client sends to')
    parser.add_argument('bytecount', type=int, nargs='?', default=16,
                        help='number of bytes for client to send (default 16)')
    parser.add_argument('-p', metavar='PORT', type=int, default=1060,
                        help='TCP port (default 1060)')
    args = parser.parse_args()
    function = choices[args.role]
    function(args.host, args.p, args.bytecount)

在我简单地在本地创建服务器之后，我启动了我的客户端

python listing3-2.py client 0.0.0.0

这是我得到的输出:

Sending 32 bytes of data, in chunks of 16 bytes
32 bytes sent

Receiving all the data the server sends back The first data received says b'CAP!CAP!CAP!CAP!CAP!CAP!CAP!CAP!' 32 bytes received

从这个输出我们知道 while() 循环已经运行了 8 次(因为有 8 个 'CAP!'s)但是 print('\r %d bytes sent' %(sent,), end=' ') 只运行了一次。对我来说更奇怪的是 sys.stdout.flush() 不起作用，尽管作者可能也注意到了这个问题。

当我尝试在有问题的 print() 之前添加一行 print('test') 时，发生了更奇怪的事情，看看会发生什么？

python listing3-2.py client 0.0.0.0

Sending 32 bytes of data, in chunks of 16 bytes test
4 bytes sent test 8 bytes sent test
12 bytes sent test
16 bytes sent test
20 bytes sent test
24 bytes sent test 28 bytes sent test
32 bytes sent Receiving all the data the server sends back The first data received says b'CAP!CAP!CAP!CAP!CAP!CAP!CAP!CAP!' 32 bytes received

在之前添加一个 print()，print('\r %d bytes sent' %(sent,), end=' ') 运行 8 次，虽然循环的结构是绝对不变的。我对添加 print() 会带来这样的后果这一事实感到非常困惑。如果在这种情况下使用 print() 方法可能会有一些奇怪的特征，我也感到困惑。

最佳答案

打印信息中的\r与end=' '组合。这是一个没有换行的回车，所以所有的行都打印在彼此之上。额外的 print 添加一个换行符并且它们停止相互打印。将其更改为 \n 以修复，或者更简单地说:

print(sent,'bytes sent')

附言还有一个数学错误:

bytecount = (bytecount + 15) // 15 * 16

应该是:

bytecount = (bytecount + 15) // 16 * 16

关于python - 尝试 TCP 连接时 while() 中出现奇怪的 print() 输出，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36114842/