socketserver --- 用于网络服务器的框架


socketserver 模块简化了编写网络服务器的任务。


class socketserver.TCPServer(server_address, RequestHandlerClass, bind_and_activate=True)

该类使用互联网 TCP 协议,它可以提供客户端与服务器之间的连续数据流。 如果 bind_and_activate 为真值,该类的构造器会自动尝试发起调用 server_bind()server_activate()。 其他形参会被传递给 BaseServer 基类。

class socketserver.UDPServer(server_address, RequestHandlerClass, bind_and_activate=True)

该类使用数据包,即一系列离散的信息分包,它们可能会无序地到达或在传输中丢失。 该类的形参与 TCPServer 的相同。

class socketserver.UnixStreamServer(server_address, RequestHandlerClass, bind_and_activate=True)
class socketserver.UnixDatagramServer(server_address, RequestHandlerClass, bind_and_activate=True)

这两个更常用的类与 TCP 和 UDP 类相似,但使用 Unix 域套接字;它们在非 Unix 系统平台上不可用。 它们的形参与 TCPServer 的相同。

这四个类会 同步地 处理请求;每个请求必须完成才能开始下一个请求。 这就不适用于每个请求要耗费很长时间来完成的情况,或者因为它需要大量的计算,又或者它返回了大量的数据而客户端处理起来很缓慢。 解决方案是创建单独的进程或线程来处理每个请求;ForkingMixInThreadingMixIn 混合类可以被用于支持异步行为。

创建一个服务器需要分几个步骤进行。 首先,你必须通过子类化 BaseRequestHandler 类并重载其 handle() 方法来创建一个请求处理句柄类;这个方法将处理传入的请求。 其次,你必须实例化某个服务器类,将服务器地址和请求处理句柄类传给它。 建议在 with 语句中使用该服务器。 然后再调用服务器对象的 handle_request()serve_forever() 方法来处理一个或多个请求。 最后,调用 server_close() 来关闭套接字(除非你使用了 with 语句)。

When inheriting from ThreadingMixIn for threaded connection behavior, you should explicitly declare how you want your threads to behave on an abrupt shutdown. The ThreadingMixIn class defines an attribute daemon_threads, which indicates whether or not the server should wait for thread termination. You should set the flag explicitly if you would like threads to behave autonomously; the default is False, meaning that Python will not exit until all threads created by ThreadingMixIn have exited.

Server classes have the same external methods and attributes, no matter what network protocol they use.

Server Creation Notes

There are five classes in an inheritance diagram, four of which represent synchronous servers of four types:

| BaseServer |
+-----------+        +------------------+
| TCPServer |------->| UnixStreamServer |
+-----------+        +------------------+
+-----------+        +--------------------+
| UDPServer |------->| UnixDatagramServer |
+-----------+        +--------------------+

Note that UnixDatagramServer derives from UDPServer, not from UnixStreamServer --- the only difference between an IP and a Unix stream server is the address family, which is simply repeated in both Unix server classes.

class socketserver.ForkingMixIn
class socketserver.ThreadingMixIn

Forking and threading versions of each type of server can be created using these mix-in classes. For instance, ThreadingUDPServer is created as follows:

class ThreadingUDPServer(ThreadingMixIn, UDPServer):

The mix-in class comes first, since it overrides a method defined in UDPServer. Setting the various attributes also changes the behavior of the underlying server mechanism.

ForkingMixIn and the Forking classes mentioned below are only available on POSIX platforms that support fork().

socketserver.ForkingMixIn.server_close() waits until all child processes complete, except if socketserver.ForkingMixIn.block_on_close attribute is false.

socketserver.ThreadingMixIn.server_close() waits until all non-daemon threads complete, except if socketserver.ThreadingMixIn.block_on_close attribute is false. Use daemonic threads by setting ThreadingMixIn.daemon_threads to True to not wait until threads complete.

3.7 版更變: socketserver.ForkingMixIn.server_close() and socketserver.ThreadingMixIn.server_close() now waits until all child processes and non-daemonic threads complete. Add a new socketserver.ForkingMixIn.block_on_close class attribute to opt-in for the pre-3.7 behaviour.

class socketserver.ForkingTCPServer
class socketserver.ForkingUDPServer
class socketserver.ThreadingTCPServer
class socketserver.ThreadingUDPServer

These classes are pre-defined using the mix-in classes.

To implement a service, you must derive a class from BaseRequestHandler and redefine its handle() method. You can then run various versions of the service by combining one of the server classes with your request handler class. The request handler class must be different for datagram or stream services. This can be hidden by using the handler subclasses StreamRequestHandler or DatagramRequestHandler.

Of course, you still have to use your head! For instance, it makes no sense to use a forking server if the service contains state in memory that can be modified by different requests, since the modifications in the child process would never reach the initial state kept in the parent process and passed to each child. In this case, you can use a threading server, but you will probably have to use locks to protect the integrity of the shared data.

On the other hand, if you are building an HTTP server where all data is stored externally (for instance, in the file system), a synchronous class will essentially render the service "deaf" while one request is being handled -- which may be for a very long time if a client is slow to receive all the data it has requested. Here a threading or forking server is appropriate.

In some cases, it may be appropriate to process part of a request synchronously, but to finish processing in a forked child depending on the request data. This can be implemented by using a synchronous server and doing an explicit fork in the request handler class handle() method.

Another approach to handling multiple simultaneous requests in an environment that supports neither threads nor fork() (or where these are too expensive or inappropriate for the service) is to maintain an explicit table of partially finished requests and to use selectors to decide which request to work on next (or whether to handle a new incoming request). This is particularly important for stream services where each client can potentially be connected for a long time (if threads or subprocesses cannot be used). See asyncore for another way to manage this.

Server 对象

class socketserver.BaseServer(server_address, RequestHandlerClass)

This is the superclass of all Server objects in the module. It defines the interface, given below, but does not implement most of the methods, which is done in subclasses. The two parameters are stored in the respective server_address and RequestHandlerClass attributes.


Return an integer file descriptor for the socket on which the server is listening. This function is most commonly passed to selectors, to allow monitoring multiple servers in the same process.


Process a single request. This function calls the following methods in order: get_request(), verify_request(), and process_request(). If the user-provided handle() method of the handler class raises an exception, the server's handle_error() method will be called. If no request is received within timeout seconds, handle_timeout() will be called and handle_request() will return.


Handle requests until an explicit shutdown() request. Poll for shutdown every poll_interval seconds. Ignores the timeout attribute. It also calls service_actions(), which may be used by a subclass or mixin to provide actions specific to a given service. For example, the ForkingMixIn class uses service_actions() to clean up zombie child processes.

3.3 版更變: Added service_actions call to the serve_forever method.


This is called in the serve_forever() loop. This method can be overridden by subclasses or mixin classes to perform actions specific to a given service, such as cleanup actions.

3.3 版新加入.


Tell the serve_forever() loop to stop and wait until it does. shutdown() must be called while serve_forever() is running in a different thread otherwise it will deadlock.


Clean up the server. May be overridden.


The family of protocols to which the server's socket belongs. Common examples are socket.AF_INET and socket.AF_UNIX.


The user-provided request handler class; an instance of this class is created for each request.


The address on which the server is listening. The format of addresses varies depending on the protocol family; see the documentation for the socket module for details. For internet protocols, this is a tuple containing a string giving the address, and an integer port number: ('', 80), for example.


The socket object on which the server will listen for incoming requests.

The server classes support the following class variables:


Whether the server will allow the reuse of an address. This defaults to False, and can be set in subclasses to change the policy.


The size of the request queue. If it takes a long time to process a single request, any requests that arrive while the server is busy are placed into a queue, up to request_queue_size requests. Once the queue is full, further requests from clients will get a "Connection denied" error. The default value is usually 5, but this can be overridden by subclasses.


The type of socket used by the server; socket.SOCK_STREAM and socket.SOCK_DGRAM are two common values.


Timeout duration, measured in seconds, or None if no timeout is desired. If handle_request() receives no incoming requests within the timeout period, the handle_timeout() method is called.

There are various server methods that can be overridden by subclasses of base server classes like TCPServer; these methods aren't useful to external users of the server object.

finish_request(request, client_address)

Actually processes the request by instantiating RequestHandlerClass and calling its handle() method.


Must accept a request from the socket, and return a 2-tuple containing the new socket object to be used to communicate with the client, and the client's address.

handle_error(request, client_address)

This function is called if the handle() method of a RequestHandlerClass instance raises an exception. The default action is to print the traceback to standard error and continue handling further requests.

3.6 版更變: Now only called for exceptions derived from the Exception class.


This function is called when the timeout attribute has been set to a value other than None and the timeout period has passed with no requests being received. The default action for forking servers is to collect the status of any child processes that have exited, while in threading servers this method does nothing.

process_request(request, client_address)

Calls finish_request() to create an instance of the RequestHandlerClass. If desired, this function can create a new process or thread to handle the request; the ForkingMixIn and ThreadingMixIn classes do this.


Called by the server's constructor to activate the server. The default behavior for a TCP server just invokes listen() on the server's socket. May be overridden.


Called by the server's constructor to bind the socket to the desired address. May be overridden.

verify_request(request, client_address)

Must return a Boolean value; if the value is True, the request will be processed, and if it's False, the request will be denied. This function can be overridden to implement access controls for a server. The default implementation always returns True.

3.6 版更變: Support for the context manager protocol was added. Exiting the context manager is equivalent to calling server_close().

Request Handler Objects

class socketserver.BaseRequestHandler

This is the superclass of all request handler objects. It defines the interface, given below. A concrete request handler subclass must define a new handle() method, and can override any of the other methods. A new instance of the subclass is created for each request.


Called before the handle() method to perform any initialization actions required. The default implementation does nothing.


This function must do all the work required to service a request. The default implementation does nothing. Several instance attributes are available to it; the request is available as self.request; the client address as self.client_address; and the server instance as self.server, in case it needs access to per-server information.

The type of self.request is different for datagram or stream services. For stream services, self.request is a socket object; for datagram services, self.request is a pair of string and socket.


Called after the handle() method to perform any clean-up actions required. The default implementation does nothing. If setup() raises an exception, this function will not be called.

class socketserver.StreamRequestHandler
class socketserver.DatagramRequestHandler

These BaseRequestHandler subclasses override the setup() and finish() methods, and provide self.rfile and self.wfile attributes. The self.rfile and self.wfile attributes can be read or written, respectively, to get the request data or return data to the client.

The rfile attributes of both classes support the io.BufferedIOBase readable interface, and DatagramRequestHandler.wfile supports the io.BufferedIOBase writable interface.

3.6 版更變: StreamRequestHandler.wfile also supports the io.BufferedIOBase writable interface.


socketserver.TCPServer 範例

This is the server side:

import socketserver

class MyTCPHandler(socketserver.BaseRequestHandler):
    The request handler class for our server.

    It is instantiated once per connection to the server, and must
    override the handle() method to implement communication to the

    def handle(self):
        # self.request is the TCP socket connected to the client = self.request.recv(1024).strip()
        print("{} wrote:".format(self.client_address[0]))
        # just send back the same data, but upper-cased

if __name__ == "__main__":
    HOST, PORT = "localhost", 9999

    # Create the server, binding to localhost on port 9999
    with socketserver.TCPServer((HOST, PORT), MyTCPHandler) as server:
        # Activate the server; this will keep running until you
        # interrupt the program with Ctrl-C

An alternative request handler class that makes use of streams (file-like objects that simplify communication by providing the standard file interface):

class MyTCPHandler(socketserver.StreamRequestHandler):

    def handle(self):
        # self.rfile is a file-like object created by the handler;
        # we can now use e.g. readline() instead of raw recv() calls = self.rfile.readline().strip()
        print("{} wrote:".format(self.client_address[0]))
        # Likewise, self.wfile is a file-like object used to write back
        # to the client

The difference is that the readline() call in the second handler will call recv() multiple times until it encounters a newline character, while the single recv() call in the first handler will just return what has been sent from the client in one sendall() call.

This is the client side:

import socket
import sys

HOST, PORT = "localhost", 9999
data = " ".join(sys.argv[1:])

# Create a socket (SOCK_STREAM means a TCP socket)
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
    # Connect to server and send data
    sock.connect((HOST, PORT))
    sock.sendall(bytes(data + "\n", "utf-8"))

    # Receive data from the server and shut down
    received = str(sock.recv(1024), "utf-8")

print("Sent:     {}".format(data))
print("Received: {}".format(received))

The output of the example should look something like this:


$ python wrote:
b'hello world with TCP' wrote:
b'python is nice'


$ python hello world with TCP
Sent:     hello world with TCP
$ python python is nice
Sent:     python is nice

socketserver.UDPServer 範例

This is the server side:

import socketserver

class MyUDPHandler(socketserver.BaseRequestHandler):
    This class works similar to the TCP handler class, except that
    self.request consists of a pair of data and client socket, and since
    there is no connection the client address must be given explicitly
    when sending data back via sendto().

    def handle(self):
        data = self.request[0].strip()
        socket = self.request[1]
        print("{} wrote:".format(self.client_address[0]))
        socket.sendto(data.upper(), self.client_address)

if __name__ == "__main__":
    HOST, PORT = "localhost", 9999
    with socketserver.UDPServer((HOST, PORT), MyUDPHandler) as server:

This is the client side:

import socket
import sys

HOST, PORT = "localhost", 9999
data = " ".join(sys.argv[1:])

# SOCK_DGRAM is the socket type to use for UDP sockets
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# As you can see, there is no connect() call; UDP has no connections.
# Instead, data is directly sent to the recipient via sendto().
sock.sendto(bytes(data + "\n", "utf-8"), (HOST, PORT))
received = str(sock.recv(1024), "utf-8")

print("Sent:     {}".format(data))
print("Received: {}".format(received))

The output of the example should look exactly like for the TCP server example.

Asynchronous Mixins

To build asynchronous handlers, use the ThreadingMixIn and ForkingMixIn classes.

An example for the ThreadingMixIn class:

import socket
import threading
import socketserver

class ThreadedTCPRequestHandler(socketserver.BaseRequestHandler):

    def handle(self):
        data = str(self.request.recv(1024), 'ascii')
        cur_thread = threading.current_thread()
        response = bytes("{}: {}".format(, data), 'ascii')

class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):

def client(ip, port, message):
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
        sock.connect((ip, port))
        sock.sendall(bytes(message, 'ascii'))
        response = str(sock.recv(1024), 'ascii')
        print("Received: {}".format(response))

if __name__ == "__main__":
    # Port 0 means to select an arbitrary unused port
    HOST, PORT = "localhost", 0

    server = ThreadedTCPServer((HOST, PORT), ThreadedTCPRequestHandler)
    with server:
        ip, port = server.server_address

        # Start a thread with the server -- that thread will then start one
        # more thread for each request
        server_thread = threading.Thread(target=server.serve_forever)
        # Exit the server thread when the main thread terminates
        server_thread.daemon = True
        print("Server loop running in thread:",

        client(ip, port, "Hello World 1")
        client(ip, port, "Hello World 2")
        client(ip, port, "Hello World 3")


The output of the example should look something like this:

$ python
Server loop running in thread: Thread-1
Received: Thread-2: Hello World 1
Received: Thread-3: Hello World 2
Received: Thread-4: Hello World 3

The ForkingMixIn class is used in the same way, except that the server will spawn a new process for each request. Available only on POSIX platforms that support fork().