python 的 socket 如何不调用 listen 方法，就只能发送数据，而不能接收数据或接受连接请求？

Question

我感觉不对啊，不 listen，也可以收和发数据呀，比如客户端的 socket，不用调用 listen，也是可读可写呀

Answer 1

listen 是给服务端用来被动监听客户端用的啊，然后需要搭配accept去使用。socket.listen() 让socket处于被动模式, 等待传入的连接和请求。如果不调用listen()，socket将无法接受传入的连接。

而且官网对这个api的解释就是这样。

socket.listen([backlog])

Enable a server to accept connections. If backlog is specified, it must be at least 0 (if it is lower, it is set to 0); it specifies the number of unaccepted connections that the system will allow before refusing new connections. If not specified, a default reasonable value is chosen.

Answer 2

看看下面的例子你就明白了：
服务器端：

import socket

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(('localhost', 12345))
server_socket.listen(5)

print("Server is listening for incoming connections...")

client_socket, client_address = server_socket.accept()
print(f"Connected to client at {client_address}")

received_data = client_socket.recv(1024).decode()
print(f"Received data from client: {received_data}")

response_data = "Hello from the server!"
client_socket.send(response_data.encode())

client_socket.close()
server_socket.close()

客户端：

import socket

client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect(('localhost', 12345))

message = "Hello from the client!"
client_socket.send(message.encode())

received_data = client_socket.recv(1024).decode()
print(f"Received data from server: {received_data}")

client_socket.close()