Python的socket模塊是網絡編程的基礎，提供低級網絡通信功能，適用於構建客戶端和服務器應用。要設置基本TCP服務器，需使用socket.socket()創(chuàng)建對象，綁定地址和端口，調用.listen()監(jiān)聽連接，並通過.accept()接受客戶端連接。構建TCP客戶端需創(chuàng)建socket對像後調用.connect()連接服務器，再使用.sendall()發(fā)送數據和??.recv()接收響應。處理多個客戶端可通過1.線程：每次連接啟動新線程；2.異步I/O：如asyncio庫實現(xiàn)無阻塞通信。注意事項包括：1.發(fā)送/接收時需編碼/解碼字符串；2.及時關閉連接以避免資源洩漏；3.測試時本地使用localhost，外部連接需綁定0.0.0.0；4.緩衝區(qū)大小可依據消息預期大小調整。掌握這些要點可為開發(fā)穩(wěn)定網絡應用打下堅實基礎。

If you're looking to get into network programming in Python, the socket module is where it starts. It gives you low-level access to network communication, which means you can build both client and server applications that send and receive data over the network. Whether you're building a chat app, handling HTTP requests manually, or experimenting with custom protocols, understanding sockets will give you solid ground to stand on.

Setting Up a Basic TCP Server

To work with TCP in Python, you'll use socket.socket() and set it up to listen for incoming connections. Here's how:

• First, import the socket module:

   import socket

• Create a socket object using socket.socket(socket.AF_INET, socket.SOCK_STREAM) — this sets up IPv4 and TCP.

• Bind it to an address and port with .bind((host, port)) . For example, 'localhost' and 12345 .

• Call .listen() to start listening for connections.

• Use .accept() in a loop to accept new clients as they connect.

Here's a minimal example:

 server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(('localhost', 12345))
server_socket.listen(1)

print("Server is listening...")
conn, addr = server_socket.accept()
print(f"Connected by {addr}")

while True:
    data = conn.recv(1024)
    if not data:
        break
    print(f"Received: {data.decode()}")
    conn.sendall(data) # Echo back the message

This creates a basic echo server — anything the client sends gets sent right back.

Building a Simple TCP Client

On the other side of the connection is the client. The client initiates communication with the server instead of waiting for it.

• Import socket again (or reuse the same script in a different environment).

• Create a socket object just like before.

• Instead of binding and listening, call .connect((host, port)) to reach out to the server.

• Then use .sendall() to send data and .recv() to read responses.

Here's a quick version:

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

message = "Hello, server!"
client_socket.sendall(message.encode())
response = client_socket.recv(1024)
print(f"Response from server: {response.decode()}")

This setup works well for simple request-response patterns. If you want to keep the connection open longer, wrap the send/receive part in a loop.

Handling Multiple Clients

Right now, our server only handles one client at a time. But what if more than one person wants to connect?

There are two main ways to handle this:

• Threading : Start a new thread each time someone connects.
• Async I/O (eg, asyncio ): Handle multiple clients without threads.

For threading, here's a quick tweak:

 import threading

def handle_client(conn, addr):
    print(f"Connected by {addr}")
    while True:
        data = conn.recv(1024)
        if not data:
            break
        print(f"Received from {addr}: {data.decode()}")
        conn.sendall(data)
    conn.close()

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

print("Server is running...")
while True:
    conn, addr = server_socket.accept()
    thread = threading.Thread(target=handle_client, args=(conn, addr))
    thread.start()

Now each client runs in its own thread, so they don't block each other. Be careful though — too many threads can cause performance issues. In those cases, look into async tools or multiplexing with select .

Some Gotchas and Tips

• Always remember to encode/decode strings when sending or receiving — sockets work with bytes, not text.
• Don't forget to close your connections when done. Leaving them open can lead to resource leaks.
• Use try/finally blocks or context managers ( with statements) to make sure sockets get cleaned up properly.
• When testing locally, localhost works fine. On real networks, you might need to bind to 0.0.0.0 to accept external connections.
• Buffer sizes like 1024 in .recv() are arbitrary — choose based on your expected message size.

Getting comfortable with these little details makes your socket code more robust and less likely to crash unexpectedly.

Basically, once you've got the basics down — setting up servers, connecting clients, handling messages — you can build all sorts of networked apps. It's not flashy, but it's powerful.

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