学习 sock 的一个问题

正在廖雪峰的网站上学习 sock 编程，代码纯手打照抄网站上的。然后当我一遍遍打开 client.py 的时候发现 server 显示来源端口在不断增大。。。是没有释放还是什么原因？

client.py

# -*- coding: utf-8 -*-

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('127.0.0.1', 9999))
print(s.recv(1024).decode('utf-8'))
for data in [b'A', b'B', b'C']:
	s.send(data)
	print(s.recv(1024).decode('utf-8'))
s.send(b'exit')
s.close()

server.py

# -*- coding: utf-8 -*-

import socket, threading, time

def tcplink(sock, addr):
	print('Accept new connection from %s:%s' % addr)
	sock.send(b'Welcome!')
	while True:
		data = sock.recv(1024)
		time.sleep(1)
		if not data or data.decode('utf-8') == 'exit':
			break
		sock.send(('Hello, %s!' % data.decode('utf-8')).encode('utf-8'))
	sock.close()
	print('Connection from %s:%s closed' % addr)

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('127.0.0.1', 9999))
s.listen(5)
print('Waiting for connection')
while True:
	sock, addr = s.accept()
	t = threading.Thread(target=tcplink, args=(sock, addr))
	t.start()

Output

Accept new connection from 127.0.0.1:59721
Accept new connection from 127.0.0.1:59722
Accept new connection from 127.0.0.1:59723
Accept new connection from 127.0.0.1:59724
Accept new connection from 127.0.0.1:59725