打印收到的服务器数据时出现问题

Question

I have the next problem: When i use this code for a EchoServer with the python asyncio library

import asyncio


class EchoServer(asyncio.Protocol):

    def connection_made(self, transport):
        self.transport = transport

    def data_received(self, data):
        print('Message received: {}'.format(data.decode()), end='')
        self.transport.write(data + b'\n')

    def connection_lost(self, exc):
        print('Client disconnected...')


loop = asyncio.get_event_loop()
coro = loop.create_server(EchoServer, '127.0.0.1', 12345)
server = loop.run_until_complete(coro)
print('Listening on {}'.format(server.sockets[0].getsockname()))

try:
    loop.run_forever()
except KeyboardInterrupt:
    pass
finally:
    server.close()
    loop.close()

in this line

print('Message received: {}'.format(data.decode()), end='')

when i use: end='' , the messages from the client without '\\n' don't log on the console and only show the messages received when client disconnected. Like this:

Message received: testMessage received: testMessage received: testClient disconnected...

this message is show only when the client disconnect.

but when i use '\\n' on the end of messages from the client the messages show on the console when the client send the messages. Like this:

Message received: test
Message received: test
Message received: test
client disconnected...

in this case in 3 diferents time and finally the client disconnect. And when i use this line:

 print('Message received: {}'.format(data.decode()))

without end='' ,works fine with the client messages without '\\n' in the end of messages.

I want to know why.

The problem isnt with the console messages format, the problem is the time when the data received are show in the console.

PS: sorry for my bad english.

Answer 1

You should manually flush stdout.

print('Message received: {}'.format(data.decode()), end='')
sys.stdout.flush()