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<div class="section" id="module-SocketServer">
<span id="socketserver-a-framework-for-network-servers"></span><h1>20.17. <a class="reference internal" href="#module-SocketServer" title="SocketServer: A framework for network servers."><tt class="xref py py-mod docutils literal"><span class="pre">SocketServer</span></tt></a> — A framework for network servers<a class="headerlink" href="#module-SocketServer" title="Permalink to this headline">¶</a></h1>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <a class="reference internal" href="#module-SocketServer" title="SocketServer: A framework for network servers."><tt class="xref py py-mod docutils literal"><span class="pre">SocketServer</span></tt></a> module has been renamed to <tt class="xref py py-mod docutils literal"><span class="pre">socketserver</span></tt> in
Python 3. The <a class="reference internal" href="../glossary.html#term-to3"><em class="xref std std-term">2to3</em></a> tool will automatically adapt imports when
converting your sources to Python 3.</p>
</div>
<p><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/2.7/Lib/SocketServer.py">Lib/SocketServer.py</a></p>
<hr class="docutils" />
<p>The <a class="reference internal" href="#module-SocketServer" title="SocketServer: A framework for network servers."><tt class="xref py py-mod docutils literal"><span class="pre">SocketServer</span></tt></a> module simplifies the task of writing network servers.</p>
<p>There are four basic server classes: <tt class="xref py py-class docutils literal"><span class="pre">TCPServer</span></tt> uses the Internet TCP
protocol, which provides for continuous streams of data between the client and
server. <tt class="xref py py-class docutils literal"><span class="pre">UDPServer</span></tt> uses datagrams, which are discrete packets of
information that may arrive out of order or be lost while in transit. The more
infrequently used <tt class="xref py py-class docutils literal"><span class="pre">UnixStreamServer</span></tt> and <tt class="xref py py-class docutils literal"><span class="pre">UnixDatagramServer</span></tt>
classes are similar, but use Unix domain sockets; they’re not available on
non-Unix platforms. For more details on network programming, consult a book
such as
W. Richard Steven’s UNIX Network Programming or Ralph Davis’s Win32 Network
Programming.</p>
<p>These four classes process requests <em class="dfn">synchronously</em>; each request must be
completed before the next request can be started. This isn’t suitable if each
request takes a long time to complete, because it requires a lot of computation,
or because it returns a lot of data which the client is slow to process. The
solution is to create a separate process or thread to handle each request; the
<tt class="xref py py-class docutils literal"><span class="pre">ForkingMixIn</span></tt> and <tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> mix-in classes can be used to
support asynchronous behaviour.</p>
<p>Creating a server requires several steps. First, you must create a request
handler class by subclassing the <tt class="xref py py-class docutils literal"><span class="pre">BaseRequestHandler</span></tt> class and
overriding its <tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt> method; this method will process incoming
requests. Second, you must instantiate one of the server classes, passing it
the server’s address and the request handler class. Finally, call the
<tt class="xref py py-meth docutils literal"><span class="pre">handle_request()</span></tt> or <tt class="xref py py-meth docutils literal"><span class="pre">serve_forever()</span></tt> method of the server object to
process one or many requests.</p>
<p>When inheriting from <tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> for threaded connection behavior,
you should explicitly declare how you want your threads to behave on an abrupt
shutdown. The <tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> class defines an attribute
<em>daemon_threads</em>, 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 <a class="reference internal" href="constants.html#False" title="False"><tt class="xref py py-const docutils literal"><span class="pre">False</span></tt></a>, meaning that Python will
not exit until all threads created by <tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> have exited.</p>
<p>Server classes have the same external methods and attributes, no matter what
network protocol they use.</p>
<div class="section" id="server-creation-notes">
<h2>20.17.1. Server Creation Notes<a class="headerlink" href="#server-creation-notes" title="Permalink to this headline">¶</a></h2>
<p>There are five classes in an inheritance diagram, four of which represent
synchronous servers of four types:</p>
<div class="highlight-python"><pre>+------------+
| BaseServer |
+------------+
|
v
+-----------+ +------------------+
| TCPServer |------->| UnixStreamServer |
+-----------+ +------------------+
|
v
+-----------+ +--------------------+
| UDPServer |------->| UnixDatagramServer |
+-----------+ +--------------------+</pre>
</div>
<p>Note that <tt class="xref py py-class docutils literal"><span class="pre">UnixDatagramServer</span></tt> derives from <tt class="xref py py-class docutils literal"><span class="pre">UDPServer</span></tt>, not from
<tt class="xref py py-class docutils literal"><span class="pre">UnixStreamServer</span></tt> — the only difference between an IP and a Unix
stream server is the address family, which is simply repeated in both Unix
server classes.</p>
<p>Forking and threading versions of each type of server can be created using the
<tt class="xref py py-class docutils literal"><span class="pre">ForkingMixIn</span></tt> and <tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> mix-in classes. For instance,
a threading UDP server class is created as follows:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">ThreadingUDPServer</span><span class="p">(</span><span class="n">ThreadingMixIn</span><span class="p">,</span> <span class="n">UDPServer</span><span class="p">):</span> <span class="k">pass</span>
</pre></div>
</div>
<p>The mix-in class must come first, since it overrides a method defined in
<tt class="xref py py-class docutils literal"><span class="pre">UDPServer</span></tt>. Setting the various attributes also change the
behavior of the underlying server mechanism.</p>
<p>To implement a service, you must derive a class from <tt class="xref py py-class docutils literal"><span class="pre">BaseRequestHandler</span></tt>
and redefine its <tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt> 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
<tt class="xref py py-class docutils literal"><span class="pre">StreamRequestHandler</span></tt> or <tt class="xref py py-class docutils literal"><span class="pre">DatagramRequestHandler</span></tt>.</p>
<p>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.</p>
<p>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.</p>
<p>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 <tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt> method.</p>
<p>Another approach to handling multiple simultaneous requests in an environment
that supports neither threads nor <tt class="xref py py-func docutils literal"><span class="pre">fork()</span></tt> (or where these are too expensive
or inappropriate for the service) is to maintain an explicit table of partially
finished requests and to use <a class="reference internal" href="select.html#module-select" title="select: Wait for I/O completion on multiple streams."><tt class="xref py py-func docutils literal"><span class="pre">select()</span></tt></a> 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 <a class="reference internal" href="asyncore.html#module-asyncore" title="asyncore: A base class for developing asynchronous socket handling services."><tt class="xref py py-mod docutils literal"><span class="pre">asyncore</span></tt></a> for
another way to manage this.</p>
</div>
<div class="section" id="server-objects">
<h2>20.17.2. Server Objects<a class="headerlink" href="#server-objects" title="Permalink to this headline">¶</a></h2>
<dl class="class">
<dt id="SocketServer.BaseServer">
<em class="property">class </em><tt class="descclassname">SocketServer.</tt><tt class="descname">BaseServer</tt><a class="headerlink" href="#SocketServer.BaseServer" title="Permalink to this definition">¶</a></dt>
<dd><p>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.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.fileno">
<tt class="descclassname">BaseServer.</tt><tt class="descname">fileno</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.fileno" title="Permalink to this definition">¶</a></dt>
<dd><p>Return an integer file descriptor for the socket on which the server is
listening. This function is most commonly passed to <a class="reference internal" href="select.html#select.select" title="select.select"><tt class="xref py py-func docutils literal"><span class="pre">select.select()</span></tt></a>, to
allow monitoring multiple servers in the same process.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.handle_request">
<tt class="descclassname">BaseServer.</tt><tt class="descname">handle_request</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.handle_request" title="Permalink to this definition">¶</a></dt>
<dd><p>Process a single request. This function calls the following methods in
order: <a class="reference internal" href="#SocketServer.BaseServer.get_request" title="SocketServer.BaseServer.get_request"><tt class="xref py py-meth docutils literal"><span class="pre">get_request()</span></tt></a>, <a class="reference internal" href="#SocketServer.BaseServer.verify_request" title="SocketServer.BaseServer.verify_request"><tt class="xref py py-meth docutils literal"><span class="pre">verify_request()</span></tt></a>, and
<a class="reference internal" href="#SocketServer.BaseServer.process_request" title="SocketServer.BaseServer.process_request"><tt class="xref py py-meth docutils literal"><span class="pre">process_request()</span></tt></a>. If the user-provided <tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt> method of the
handler class raises an exception, the server’s <a class="reference internal" href="#SocketServer.BaseServer.handle_error" title="SocketServer.BaseServer.handle_error"><tt class="xref py py-meth docutils literal"><span class="pre">handle_error()</span></tt></a> method
will be called. If no request is received within <tt class="xref py py-attr docutils literal"><span class="pre">self.timeout</span></tt>
seconds, <a class="reference internal" href="#SocketServer.BaseServer.handle_timeout" title="SocketServer.BaseServer.handle_timeout"><tt class="xref py py-meth docutils literal"><span class="pre">handle_timeout()</span></tt></a> will be called and <a class="reference internal" href="#SocketServer.BaseServer.handle_request" title="SocketServer.BaseServer.handle_request"><tt class="xref py py-meth docutils literal"><span class="pre">handle_request()</span></tt></a>
will return.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.serve_forever">
<tt class="descclassname">BaseServer.</tt><tt class="descname">serve_forever</tt><big>(</big><em>poll_interval=0.5</em><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.serve_forever" title="Permalink to this definition">¶</a></dt>
<dd><p>Handle requests until an explicit <a class="reference internal" href="#SocketServer.BaseServer.shutdown" title="SocketServer.BaseServer.shutdown"><tt class="xref py py-meth docutils literal"><span class="pre">shutdown()</span></tt></a> request.
Poll for shutdown every <em>poll_interval</em> seconds. Ignores <tt class="xref py py-attr docutils literal"><span class="pre">self.timeout</span></tt>.
If you need to do periodic tasks, do them in another thread.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.shutdown">
<tt class="descclassname">BaseServer.</tt><tt class="descname">shutdown</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.shutdown" title="Permalink to this definition">¶</a></dt>
<dd><p>Tell the <a class="reference internal" href="#SocketServer.BaseServer.serve_forever" title="SocketServer.BaseServer.serve_forever"><tt class="xref py py-meth docutils literal"><span class="pre">serve_forever()</span></tt></a> loop to stop and wait until it does.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="attribute">
<dt id="SocketServer.BaseServer.address_family">
<tt class="descclassname">BaseServer.</tt><tt class="descname">address_family</tt><a class="headerlink" href="#SocketServer.BaseServer.address_family" title="Permalink to this definition">¶</a></dt>
<dd><p>The family of protocols to which the server’s socket belongs.
Common examples are <a class="reference internal" href="socket.html#socket.AF_INET" title="socket.AF_INET"><tt class="xref py py-const docutils literal"><span class="pre">socket.AF_INET</span></tt></a> and <a class="reference internal" href="socket.html#socket.AF_UNIX" title="socket.AF_UNIX"><tt class="xref py py-const docutils literal"><span class="pre">socket.AF_UNIX</span></tt></a>.</p>
</dd></dl>
<dl class="attribute">
<dt id="SocketServer.BaseServer.RequestHandlerClass">
<tt class="descclassname">BaseServer.</tt><tt class="descname">RequestHandlerClass</tt><a class="headerlink" href="#SocketServer.BaseServer.RequestHandlerClass" title="Permalink to this definition">¶</a></dt>
<dd><p>The user-provided request handler class; an instance of this class is created
for each request.</p>
</dd></dl>
<dl class="attribute">
<dt id="SocketServer.BaseServer.server_address">
<tt class="descclassname">BaseServer.</tt><tt class="descname">server_address</tt><a class="headerlink" href="#SocketServer.BaseServer.server_address" title="Permalink to this definition">¶</a></dt>
<dd><p>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: <tt class="docutils literal"><span class="pre">('127.0.0.1',</span> <span class="pre">80)</span></tt>, for example.</p>
</dd></dl>
<dl class="attribute">
<dt id="SocketServer.BaseServer.socket">
<tt class="descclassname">BaseServer.</tt><tt class="descname">socket</tt><a class="headerlink" href="#SocketServer.BaseServer.socket" title="Permalink to this definition">¶</a></dt>
<dd><p>The socket object on which the server will listen for incoming requests.</p>
</dd></dl>
<p>The server classes support the following class variables:</p>
<dl class="attribute">
<dt id="SocketServer.BaseServer.allow_reuse_address">
<tt class="descclassname">BaseServer.</tt><tt class="descname">allow_reuse_address</tt><a class="headerlink" href="#SocketServer.BaseServer.allow_reuse_address" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether the server will allow the reuse of an address. This defaults to
<a class="reference internal" href="constants.html#False" title="False"><tt class="xref py py-const docutils literal"><span class="pre">False</span></tt></a>, and can be set in subclasses to change the policy.</p>
</dd></dl>
<dl class="attribute">
<dt id="SocketServer.BaseServer.request_queue_size">
<tt class="descclassname">BaseServer.</tt><tt class="descname">request_queue_size</tt><a class="headerlink" href="#SocketServer.BaseServer.request_queue_size" title="Permalink to this definition">¶</a></dt>
<dd><p>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 <a class="reference internal" href="#SocketServer.BaseServer.request_queue_size" title="SocketServer.BaseServer.request_queue_size"><tt class="xref py py-attr docutils literal"><span class="pre">request_queue_size</span></tt></a> 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.</p>
</dd></dl>
<dl class="attribute">
<dt id="SocketServer.BaseServer.socket_type">
<tt class="descclassname">BaseServer.</tt><tt class="descname">socket_type</tt><a class="headerlink" href="#SocketServer.BaseServer.socket_type" title="Permalink to this definition">¶</a></dt>
<dd><p>The type of socket used by the server; <a class="reference internal" href="socket.html#socket.SOCK_STREAM" title="socket.SOCK_STREAM"><tt class="xref py py-const docutils literal"><span class="pre">socket.SOCK_STREAM</span></tt></a> and
<a class="reference internal" href="socket.html#socket.SOCK_DGRAM" title="socket.SOCK_DGRAM"><tt class="xref py py-const docutils literal"><span class="pre">socket.SOCK_DGRAM</span></tt></a> are two common values.</p>
</dd></dl>
<dl class="attribute">
<dt id="SocketServer.BaseServer.timeout">
<tt class="descclassname">BaseServer.</tt><tt class="descname">timeout</tt><a class="headerlink" href="#SocketServer.BaseServer.timeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Timeout duration, measured in seconds, or <a class="reference internal" href="constants.html#None" title="None"><tt class="xref py py-const docutils literal"><span class="pre">None</span></tt></a> if no timeout is
desired. If <a class="reference internal" href="#SocketServer.BaseServer.handle_request" title="SocketServer.BaseServer.handle_request"><tt class="xref py py-meth docutils literal"><span class="pre">handle_request()</span></tt></a> receives no incoming requests within the
timeout period, the <a class="reference internal" href="#SocketServer.BaseServer.handle_timeout" title="SocketServer.BaseServer.handle_timeout"><tt class="xref py py-meth docutils literal"><span class="pre">handle_timeout()</span></tt></a> method is called.</p>
</dd></dl>
<p>There are various server methods that can be overridden by subclasses of base
server classes like <tt class="xref py py-class docutils literal"><span class="pre">TCPServer</span></tt>; these methods aren’t useful to external
users of the server object.</p>
<dl class="method">
<dt id="SocketServer.BaseServer.finish_request">
<tt class="descclassname">BaseServer.</tt><tt class="descname">finish_request</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.finish_request" title="Permalink to this definition">¶</a></dt>
<dd><p>Actually processes the request by instantiating <a class="reference internal" href="#SocketServer.BaseServer.RequestHandlerClass" title="SocketServer.BaseServer.RequestHandlerClass"><tt class="xref py py-attr docutils literal"><span class="pre">RequestHandlerClass</span></tt></a> and
calling its <tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt> method.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.get_request">
<tt class="descclassname">BaseServer.</tt><tt class="descname">get_request</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.get_request" title="Permalink to this definition">¶</a></dt>
<dd><p>Must accept a request from the socket, and return a 2-tuple containing the <em>new</em>
socket object to be used to communicate with the client, and the client’s
address.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.handle_error">
<tt class="descclassname">BaseServer.</tt><tt class="descname">handle_error</tt><big>(</big><em>request</em>, <em>client_address</em><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.handle_error" title="Permalink to this definition">¶</a></dt>
<dd><p>This function is called if the <a class="reference internal" href="#SocketServer.BaseServer.RequestHandlerClass" title="SocketServer.BaseServer.RequestHandlerClass"><tt class="xref py py-attr docutils literal"><span class="pre">RequestHandlerClass</span></tt></a>‘s <tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt>
method raises an exception. The default action is to print the traceback to
standard output and continue handling further requests.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.handle_timeout">
<tt class="descclassname">BaseServer.</tt><tt class="descname">handle_timeout</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.handle_timeout" title="Permalink to this definition">¶</a></dt>
<dd><p>This function is called when the <a class="reference internal" href="#SocketServer.BaseServer.timeout" title="SocketServer.BaseServer.timeout"><tt class="xref py py-attr docutils literal"><span class="pre">timeout</span></tt></a> attribute has been set to a
value other than <a class="reference internal" href="constants.html#None" title="None"><tt class="xref py py-const docutils literal"><span class="pre">None</span></tt></a> 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.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.process_request">
<tt class="descclassname">BaseServer.</tt><tt class="descname">process_request</tt><big>(</big><em>request</em>, <em>client_address</em><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.process_request" title="Permalink to this definition">¶</a></dt>
<dd><p>Calls <a class="reference internal" href="#SocketServer.BaseServer.finish_request" title="SocketServer.BaseServer.finish_request"><tt class="xref py py-meth docutils literal"><span class="pre">finish_request()</span></tt></a> to create an instance of the
<a class="reference internal" href="#SocketServer.BaseServer.RequestHandlerClass" title="SocketServer.BaseServer.RequestHandlerClass"><tt class="xref py py-attr docutils literal"><span class="pre">RequestHandlerClass</span></tt></a>. If desired, this function can create a new process
or thread to handle the request; the <tt class="xref py py-class docutils literal"><span class="pre">ForkingMixIn</span></tt> and
<tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> classes do this.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.server_activate">
<tt class="descclassname">BaseServer.</tt><tt class="descname">server_activate</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.server_activate" title="Permalink to this definition">¶</a></dt>
<dd><p>Called by the server’s constructor to activate the server. The default behavior
just <tt class="xref py py-meth docutils literal"><span class="pre">listen()</span></tt>s to the server’s socket. May be overridden.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.server_bind">
<tt class="descclassname">BaseServer.</tt><tt class="descname">server_bind</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.server_bind" title="Permalink to this definition">¶</a></dt>
<dd><p>Called by the server’s constructor to bind the socket to the desired address.
May be overridden.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.BaseServer.verify_request">
<tt class="descclassname">BaseServer.</tt><tt class="descname">verify_request</tt><big>(</big><em>request</em>, <em>client_address</em><big>)</big><a class="headerlink" href="#SocketServer.BaseServer.verify_request" title="Permalink to this definition">¶</a></dt>
<dd><p>Must return a Boolean value; if the value is <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const docutils literal"><span class="pre">True</span></tt></a>, the request will be
processed, and if it’s <a class="reference internal" href="constants.html#False" title="False"><tt class="xref py py-const docutils literal"><span class="pre">False</span></tt></a>, the request will be denied. This function
can be overridden to implement access controls for a server. The default
implementation always returns <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const docutils literal"><span class="pre">True</span></tt></a>.</p>
</dd></dl>
</div>
<div class="section" id="requesthandler-objects">
<h2>20.17.3. RequestHandler Objects<a class="headerlink" href="#requesthandler-objects" title="Permalink to this headline">¶</a></h2>
<p>The request handler class must define a new <tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt> method, and can
override any of the following methods. A new instance is created for each
request.</p>
<dl class="method">
<dt id="SocketServer.RequestHandler.finish">
<tt class="descclassname">RequestHandler.</tt><tt class="descname">finish</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.RequestHandler.finish" title="Permalink to this definition">¶</a></dt>
<dd><p>Called after the <a class="reference internal" href="#SocketServer.RequestHandler.handle" title="SocketServer.RequestHandler.handle"><tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt></a> method to perform any clean-up actions
required. The default implementation does nothing. If <a class="reference internal" href="#SocketServer.RequestHandler.setup" title="SocketServer.RequestHandler.setup"><tt class="xref py py-meth docutils literal"><span class="pre">setup()</span></tt></a>
raises an exception, this function will not be called.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.RequestHandler.handle">
<tt class="descclassname">RequestHandler.</tt><tt class="descname">handle</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.RequestHandler.handle" title="Permalink to this definition">¶</a></dt>
<dd><p>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 <tt class="xref py py-attr docutils literal"><span class="pre">self.request</span></tt>; the client
address as <tt class="xref py py-attr docutils literal"><span class="pre">self.client_address</span></tt>; and the server instance as
<tt class="xref py py-attr docutils literal"><span class="pre">self.server</span></tt>, in case it needs access to per-server information.</p>
<p>The type of <tt class="xref py py-attr docutils literal"><span class="pre">self.request</span></tt> is different for datagram or stream
services. For stream services, <tt class="xref py py-attr docutils literal"><span class="pre">self.request</span></tt> is a socket object; for
datagram services, <tt class="xref py py-attr docutils literal"><span class="pre">self.request</span></tt> is a pair of string and socket.
However, this can be hidden by using the request handler subclasses
<tt class="xref py py-class docutils literal"><span class="pre">StreamRequestHandler</span></tt> or <tt class="xref py py-class docutils literal"><span class="pre">DatagramRequestHandler</span></tt>, which
override the <a class="reference internal" href="#SocketServer.RequestHandler.setup" title="SocketServer.RequestHandler.setup"><tt class="xref py py-meth docutils literal"><span class="pre">setup()</span></tt></a> and <a class="reference internal" href="#SocketServer.RequestHandler.finish" title="SocketServer.RequestHandler.finish"><tt class="xref py py-meth docutils literal"><span class="pre">finish()</span></tt></a> methods, and provide
<tt class="xref py py-attr docutils literal"><span class="pre">self.rfile</span></tt> and <tt class="xref py py-attr docutils literal"><span class="pre">self.wfile</span></tt> attributes. <tt class="xref py py-attr docutils literal"><span class="pre">self.rfile</span></tt> and
<tt class="xref py py-attr docutils literal"><span class="pre">self.wfile</span></tt> can be read or written, respectively, to get the request
data or return data to the client.</p>
</dd></dl>
<dl class="method">
<dt id="SocketServer.RequestHandler.setup">
<tt class="descclassname">RequestHandler.</tt><tt class="descname">setup</tt><big>(</big><big>)</big><a class="headerlink" href="#SocketServer.RequestHandler.setup" title="Permalink to this definition">¶</a></dt>
<dd><p>Called before the <a class="reference internal" href="#SocketServer.RequestHandler.handle" title="SocketServer.RequestHandler.handle"><tt class="xref py py-meth docutils literal"><span class="pre">handle()</span></tt></a> method to perform any initialization actions
required. The default implementation does nothing.</p>
</dd></dl>
</div>
<div class="section" id="examples">
<h2>20.17.4. Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="section" id="socketserver-tcpserver-example">
<h3>20.17.4.1. <tt class="xref py py-class docutils literal"><span class="pre">SocketServer.TCPServer</span></tt> Example<a class="headerlink" href="#socketserver-tcpserver-example" title="Permalink to this headline">¶</a></h3>
<p>This is the server side:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">SocketServer</span>
<span class="k">class</span> <span class="nc">MyTCPHandler</span><span class="p">(</span><span class="n">SocketServer</span><span class="o">.</span><span class="n">BaseRequestHandler</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> The RequestHandler class for our server.</span>
<span class="sd"> It is instantiated once per connection to the server, and must</span>
<span class="sd"> override the handle() method to implement communication to the</span>
<span class="sd"> client.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">handle</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c"># self.request is the TCP socket connected to the client</span>
<span class="bp">self</span><span class="o">.</span><span class="n">data</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1024</span><span class="p">)</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
<span class="k">print</span> <span class="s">"{} wrote:"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">client_address</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="k">print</span> <span class="bp">self</span><span class="o">.</span><span class="n">data</span>
<span class="c"># just send back the same data, but upper-cased</span>
<span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">data</span><span class="o">.</span><span class="n">upper</span><span class="p">())</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">"__main__"</span><span class="p">:</span>
<span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span> <span class="o">=</span> <span class="s">"localhost"</span><span class="p">,</span> <span class="mi">9999</span>
<span class="c"># Create the server, binding to localhost on port 9999</span>
<span class="n">server</span> <span class="o">=</span> <span class="n">SocketServer</span><span class="o">.</span><span class="n">TCPServer</span><span class="p">((</span><span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span><span class="p">),</span> <span class="n">MyTCPHandler</span><span class="p">)</span>
<span class="c"># Activate the server; this will keep running until you</span>
<span class="c"># interrupt the program with Ctrl-C</span>
<span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">()</span>
</pre></div>
</div>
<p>An alternative request handler class that makes use of streams (file-like
objects that simplify communication by providing the standard file interface):</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">MyTCPHandler</span><span class="p">(</span><span class="n">SocketServer</span><span class="o">.</span><span class="n">StreamRequestHandler</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">handle</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c"># self.rfile is a file-like object created by the handler;</span>
<span class="c"># we can now use e.g. readline() instead of raw recv() calls</span>
<span class="bp">self</span><span class="o">.</span><span class="n">data</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">rfile</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
<span class="k">print</span> <span class="s">"{} wrote:"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">client_address</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="k">print</span> <span class="bp">self</span><span class="o">.</span><span class="n">data</span>
<span class="c"># Likewise, self.wfile is a file-like object used to write back</span>
<span class="c"># to the client</span>
<span class="bp">self</span><span class="o">.</span><span class="n">wfile</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">data</span><span class="o">.</span><span class="n">upper</span><span class="p">())</span>
</pre></div>
</div>
<p>The difference is that the <tt class="docutils literal"><span class="pre">readline()</span></tt> call in the second handler will call
<tt class="docutils literal"><span class="pre">recv()</span></tt> multiple times until it encounters a newline character, while the
single <tt class="docutils literal"><span class="pre">recv()</span></tt> call in the first handler will just return what has been sent
from the client in one <tt class="docutils literal"><span class="pre">sendall()</span></tt> call.</p>
<p>This is the client side:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">socket</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span> <span class="o">=</span> <span class="s">"localhost"</span><span class="p">,</span> <span class="mi">9999</span>
<span class="n">data</span> <span class="o">=</span> <span class="s">" "</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">:])</span>
<span class="c"># Create a socket (SOCK_STREAM means a TCP socket)</span>
<span class="n">sock</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">AF_INET</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">SOCK_STREAM</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="c"># Connect to server and send data</span>
<span class="n">sock</span><span class="o">.</span><span class="n">connect</span><span class="p">((</span><span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span><span class="p">))</span>
<span class="n">sock</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="n">data</span> <span class="o">+</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">)</span>
<span class="c"># Receive data from the server and shut down</span>
<span class="n">received</span> <span class="o">=</span> <span class="n">sock</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1024</span><span class="p">)</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">sock</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">print</span> <span class="s">"Sent: {}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="k">print</span> <span class="s">"Received: {}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">received</span><span class="p">)</span>
</pre></div>
</div>
<p>The output of the example should look something like this:</p>
<p>Server:</p>
<div class="highlight-python"><pre>$ python TCPServer.py
127.0.0.1 wrote:
hello world with TCP
127.0.0.1 wrote:
python is nice</pre>
</div>
<p>Client:</p>
<div class="highlight-python"><pre>$ python TCPClient.py hello world with TCP
Sent: hello world with TCP
Received: HELLO WORLD WITH TCP
$ python TCPClient.py python is nice
Sent: python is nice
Received: PYTHON IS NICE</pre>
</div>
</div>
<div class="section" id="socketserver-udpserver-example">
<h3>20.17.4.2. <tt class="xref py py-class docutils literal"><span class="pre">SocketServer.UDPServer</span></tt> Example<a class="headerlink" href="#socketserver-udpserver-example" title="Permalink to this headline">¶</a></h3>
<p>This is the server side:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">SocketServer</span>
<span class="k">class</span> <span class="nc">MyUDPHandler</span><span class="p">(</span><span class="n">SocketServer</span><span class="o">.</span><span class="n">BaseRequestHandler</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> This class works similar to the TCP handler class, except that</span>
<span class="sd"> self.request consists of a pair of data and client socket, and since</span>
<span class="sd"> there is no connection the client address must be given explicitly</span>
<span class="sd"> when sending data back via sendto().</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">handle</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">data</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
<span class="n">socket</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>
<span class="k">print</span> <span class="s">"{} wrote:"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">client_address</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="k">print</span> <span class="n">data</span>
<span class="n">socket</span><span class="o">.</span><span class="n">sendto</span><span class="p">(</span><span class="n">data</span><span class="o">.</span><span class="n">upper</span><span class="p">(),</span> <span class="bp">self</span><span class="o">.</span><span class="n">client_address</span><span class="p">)</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">"__main__"</span><span class="p">:</span>
<span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span> <span class="o">=</span> <span class="s">"localhost"</span><span class="p">,</span> <span class="mi">9999</span>
<span class="n">server</span> <span class="o">=</span> <span class="n">SocketServer</span><span class="o">.</span><span class="n">UDPServer</span><span class="p">((</span><span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span><span class="p">),</span> <span class="n">MyUDPHandler</span><span class="p">)</span>
<span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">()</span>
</pre></div>
</div>
<p>This is the client side:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">socket</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span> <span class="o">=</span> <span class="s">"localhost"</span><span class="p">,</span> <span class="mi">9999</span>
<span class="n">data</span> <span class="o">=</span> <span class="s">" "</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">:])</span>
<span class="c"># SOCK_DGRAM is the socket type to use for UDP sockets</span>
<span class="n">sock</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">AF_INET</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">SOCK_DGRAM</span><span class="p">)</span>
<span class="c"># As you can see, there is no connect() call; UDP has no connections.</span>
<span class="c"># Instead, data is directly sent to the recipient via sendto().</span>
<span class="n">sock</span><span class="o">.</span><span class="n">sendto</span><span class="p">(</span><span class="n">data</span> <span class="o">+</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="p">(</span><span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span><span class="p">))</span>
<span class="n">received</span> <span class="o">=</span> <span class="n">sock</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1024</span><span class="p">)</span>
<span class="k">print</span> <span class="s">"Sent: {}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="k">print</span> <span class="s">"Received: {}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">received</span><span class="p">)</span>
</pre></div>
</div>
<p>The output of the example should look exactly like for the TCP server example.</p>
</div>
<div class="section" id="asynchronous-mixins">
<h3>20.17.4.3. Asynchronous Mixins<a class="headerlink" href="#asynchronous-mixins" title="Permalink to this headline">¶</a></h3>
<p>To build asynchronous handlers, use the <tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> and
<tt class="xref py py-class docutils literal"><span class="pre">ForkingMixIn</span></tt> classes.</p>
<p>An example for the <tt class="xref py py-class docutils literal"><span class="pre">ThreadingMixIn</span></tt> class:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">socket</span>
<span class="kn">import</span> <span class="nn">threading</span>
<span class="kn">import</span> <span class="nn">SocketServer</span>
<span class="k">class</span> <span class="nc">ThreadedTCPRequestHandler</span><span class="p">(</span><span class="n">SocketServer</span><span class="o">.</span><span class="n">BaseRequestHandler</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">handle</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">data</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1024</span><span class="p">)</span>
<span class="n">cur_thread</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">current_thread</span><span class="p">()</span>
<span class="n">response</span> <span class="o">=</span> <span class="s">"{}: {}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">cur_thread</span><span class="o">.</span><span class="n">name</span><span class="p">,</span> <span class="n">data</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="n">response</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">ThreadedTCPServer</span><span class="p">(</span><span class="n">SocketServer</span><span class="o">.</span><span class="n">ThreadingMixIn</span><span class="p">,</span> <span class="n">SocketServer</span><span class="o">.</span><span class="n">TCPServer</span><span class="p">):</span>
<span class="k">pass</span>
<span class="k">def</span> <span class="nf">client</span><span class="p">(</span><span class="n">ip</span><span class="p">,</span> <span class="n">port</span><span class="p">,</span> <span class="n">message</span><span class="p">):</span>
<span class="n">sock</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">AF_INET</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">SOCK_STREAM</span><span class="p">)</span>
<span class="n">sock</span><span class="o">.</span><span class="n">connect</span><span class="p">((</span><span class="n">ip</span><span class="p">,</span> <span class="n">port</span><span class="p">))</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">sock</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="n">message</span><span class="p">)</span>
<span class="n">response</span> <span class="o">=</span> <span class="n">sock</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1024</span><span class="p">)</span>
<span class="k">print</span> <span class="s">"Received: {}"</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">response</span><span class="p">)</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">sock</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">"__main__"</span><span class="p">:</span>
<span class="c"># Port 0 means to select an arbitrary unused port</span>
<span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span> <span class="o">=</span> <span class="s">"localhost"</span><span class="p">,</span> <span class="mi">0</span>
<span class="n">server</span> <span class="o">=</span> <span class="n">ThreadedTCPServer</span><span class="p">((</span><span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span><span class="p">),</span> <span class="n">ThreadedTCPRequestHandler</span><span class="p">)</span>
<span class="n">ip</span><span class="p">,</span> <span class="n">port</span> <span class="o">=</span> <span class="n">server</span><span class="o">.</span><span class="n">server_address</span>
<span class="c"># Start a thread with the server -- that thread will then start one</span>
<span class="c"># more thread for each request</span>
<span class="n">server_thread</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">)</span>
<span class="c"># Exit the server thread when the main thread terminates</span>
<span class="n">server_thread</span><span class="o">.</span><span class="n">daemon</span> <span class="o">=</span> <span class="bp">True</span>
<span class="n">server_thread</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="k">print</span> <span class="s">"Server loop running in thread:"</span><span class="p">,</span> <span class="n">server_thread</span><span class="o">.</span><span class="n">name</span>
<span class="n">client</span><span class="p">(</span><span class="n">ip</span><span class="p">,</span> <span class="n">port</span><span class="p">,</span> <span class="s">"Hello World 1"</span><span class="p">)</span>
<span class="n">client</span><span class="p">(</span><span class="n">ip</span><span class="p">,</span> <span class="n">port</span><span class="p">,</span> <span class="s">"Hello World 2"</span><span class="p">)</span>
<span class="n">client</span><span class="p">(</span><span class="n">ip</span><span class="p">,</span> <span class="n">port</span><span class="p">,</span> <span class="s">"Hello World 3"</span><span class="p">)</span>
<span class="n">server</span><span class="o">.</span><span class="n">shutdown</span><span class="p">()</span>
</pre></div>
</div>
<p>The output of the example should look something like this:</p>
<div class="highlight-python"><pre>$ python ThreadedTCPServer.py
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</pre>
</div>
<p>The <tt class="xref py py-class docutils literal"><span class="pre">ForkingMixIn</span></tt> class is used in the same way, except that the server
will spawn a new process for each request.</p>
</div>
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<li><a class="reference internal" href="#">20.17. <tt class="docutils literal"><span class="pre">SocketServer</span></tt> — A framework for network servers</a><ul>
<li><a class="reference internal" href="#server-creation-notes">20.17.1. Server Creation Notes</a></li>
<li><a class="reference internal" href="#server-objects">20.17.2. Server Objects</a></li>
<li><a class="reference internal" href="#requesthandler-objects">20.17.3. RequestHandler Objects</a></li>
<li><a class="reference internal" href="#examples">20.17.4. Examples</a><ul>
<li><a class="reference internal" href="#socketserver-tcpserver-example">20.17.4.1. <tt class="docutils literal"><span class="pre">SocketServer.TCPServer</span></tt> Example</a></li>
<li><a class="reference internal" href="#socketserver-udpserver-example">20.17.4.2. <tt class="docutils literal"><span class="pre">SocketServer.UDPServer</span></tt> Example</a></li>
<li><a class="reference internal" href="#asynchronous-mixins">20.17.4.3. Asynchronous Mixins</a></li>
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