Python udp socket.recv将从哪个数据包接收？

Question

I just started working with udp in python, and came up with the following client for talking back and forth with the server I'm writing. My question is about the recvfrom call. What packets will it receive? Will it get any packets or is there some registration that happens that says I want the results from the thing I sent to? I'm more curious about it at lower level, like what syscalls are being made.

#!/usr/bin/python3
# shell.py
#
# Usage:
#
#       ./shell.py <IP_ADDR> <PORT>


import sys
import socket

SERVER_IP = sys.argv[1]
SERVER_PORT = int(sys.argv[2])
MAX_MESSAGE_LEN = 4096

# set up the right socket type

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
target = (SERVER_IP, SERVER_PORT)

try:
    while True:
        data = input("> ")
        sent = sock.sendto(data.encode('utf-8'), target)

        data, server = sock.recvfrom(MAX_MESSAGE_LEN)

        print(repr(server))
        print("Got {}".format(data))
finally:
    print("Closing socket")
    sock.close()

Answer 1

socket.recvfrom is implemented in C here:

https://github.com/python/cpython/blob/master/Modules/socketmodule.c#L3525

if you want to know exactly what it is doing.

To answer the other part of your question, UDP is connectionless, so there is no handshaking or registration involved. It will read any data you send to that port.