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<div class="section" id="module-socket">
<h1>18.2. <tt class="xref docutils literal"><span class="pre">socket</span></tt> — Low-level networking interface<a class="headerlink" href="#module-socket" title="Permalink to this headline">¶</a></h1>
<p>This module provides access to the BSD <em>socket</em> interface. It is available on
all modern Unix systems, Windows, Mac OS X, BeOS, OS/2, and probably additional
platforms.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Some behavior may be platform dependent, since calls are made to the operating
system socket APIs.</p>
</div>
<p>For an introduction to socket programming (in C), see the following papers: An
Introductory 4.3BSD Interprocess Communication Tutorial, by Stuart Sechrest and
An Advanced 4.3BSD Interprocess Communication Tutorial, by Samuel J. Leffler et
al, both in the UNIX Programmer’s Manual, Supplementary Documents 1 (sections
PS1:7 and PS1:8). The platform-specific reference material for the various
socket-related system calls are also a valuable source of information on the
details of socket semantics. For Unix, refer to the manual pages; for Windows,
see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may
want to refer to <span class="target" id="index-562"></span><a class="reference external" href="http://tools.ietf.org/html/rfc3493.html"><strong>RFC 3493</strong></a> titled Basic Socket Interface Extensions for IPv6.</p>
<p id="index-563">The Python interface is a straightforward transliteration of the Unix system
call and library interface for sockets to Python’s object-oriented style: the
<a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a> function returns a <em>socket object</em> whose methods implement
the various socket system calls. Parameter types are somewhat higher-level than
in the C interface: as with <tt class="xref docutils literal"><span class="pre">read()</span></tt> and <tt class="xref docutils literal"><span class="pre">write()</span></tt> operations on Python
files, buffer allocation on receive operations is automatic, and buffer length
is implicit on send operations.</p>
<p>Socket addresses are represented as follows: A single string is used for the
<a title="socket.AF_UNIX" class="reference internal" href="#socket.AF_UNIX"><tt class="xref docutils literal"><span class="pre">AF_UNIX</span></tt></a> address family. A pair <tt class="docutils literal"><span class="pre">(host,</span> <span class="pre">port)</span></tt> is used for the
<a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a> address family, where <em>host</em> is a string representing either a
hostname in Internet domain notation like <tt class="docutils literal"><span class="pre">'daring.cwi.nl'</span></tt> or an IPv4 address
like <tt class="docutils literal"><span class="pre">'100.50.200.5'</span></tt>, and <em>port</em> is an integral port number. For
<a title="socket.AF_INET6" class="reference internal" href="#socket.AF_INET6"><tt class="xref docutils literal"><span class="pre">AF_INET6</span></tt></a> address family, a four-tuple <tt class="docutils literal"><span class="pre">(host,</span> <span class="pre">port,</span> <span class="pre">flowinfo,</span>
<span class="pre">scopeid)</span></tt> is used, where <em>flowinfo</em> and <em>scopeid</em> represents <tt class="docutils literal"><span class="pre">sin6_flowinfo</span></tt>
and <tt class="docutils literal"><span class="pre">sin6_scope_id</span></tt> member in <tt class="xref docutils literal"><span class="pre">struct</span> <span class="pre">sockaddr_in6</span></tt> in C. For
<tt class="xref docutils literal"><span class="pre">socket</span></tt> module methods, <em>flowinfo</em> and <em>scopeid</em> can be omitted just for
backward compatibility. Note, however, omission of <em>scopeid</em> can cause problems
in manipulating scoped IPv6 addresses. Other address families are currently not
supported. The address format required by a particular socket object is
automatically selected based on the address family specified when the socket
object was created.</p>
<p>For IPv4 addresses, two special forms are accepted instead of a host address:
the empty string represents <tt class="xref docutils literal"><span class="pre">INADDR_ANY</span></tt>, and the string
<tt class="docutils literal"><span class="pre">'<broadcast>'</span></tt> represents <tt class="xref docutils literal"><span class="pre">INADDR_BROADCAST</span></tt>. The behavior is not
available for IPv6 for backward compatibility, therefore, you may want to avoid
these if you intend to support IPv6 with your Python programs.</p>
<p>If you use a hostname in the <em>host</em> portion of IPv4/v6 socket address, the
program may show a nondeterministic behavior, as Python uses the first address
returned from the DNS resolution. The socket address will be resolved
differently into an actual IPv4/v6 address, depending on the results from DNS
resolution and/or the host configuration. For deterministic behavior use a
numeric address in <em>host</em> portion.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5: </span>AF_NETLINK sockets are represented as pairs <tt class="docutils literal"><span class="pre">pid,</span> <span class="pre">groups</span></tt>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6: </span>Linux-only support for TIPC is also available using the <tt class="xref docutils literal"><span class="pre">AF_TIPC</span></tt>
address family. TIPC is an open, non-IP based networked protocol designed
for use in clustered computer environments. Addresses are represented by a
tuple, and the fields depend on the address type. The general tuple form is
<tt class="docutils literal"><span class="pre">(addr_type,</span> <span class="pre">v1,</span> <span class="pre">v2,</span> <span class="pre">v3</span> <span class="pre">[,</span> <span class="pre">scope])</span></tt>, where:<blockquote>
<ul>
<li><p class="first"><em>addr_type</em> is one of TIPC_ADDR_NAMESEQ, TIPC_ADDR_NAME, or
TIPC_ADDR_ID.</p>
</li>
<li><p class="first"><em>scope</em> is one of TIPC_ZONE_SCOPE, TIPC_CLUSTER_SCOPE, and
TIPC_NODE_SCOPE.</p>
</li>
<li><p class="first">If <em>addr_type</em> is TIPC_ADDR_NAME, then <em>v1</em> is the server type, <em>v2</em> is
the port identifier, and <em>v3</em> should be 0.</p>
<p>If <em>addr_type</em> is TIPC_ADDR_NAMESEQ, then <em>v1</em> is the server type, <em>v2</em>
is the lower port number, and <em>v3</em> is the upper port number.</p>
<p>If <em>addr_type</em> is TIPC_ADDR_ID, then <em>v1</em> is the node, <em>v2</em> is the
reference, and <em>v3</em> should be set to 0.</p>
</li>
</ul>
</blockquote>
</p>
<p>All errors raise exceptions. The normal exceptions for invalid argument types
and out-of-memory conditions can be raised; errors related to socket or address
semantics raise the error <a title="socket.error" class="reference internal" href="#socket.error"><tt class="xref docutils literal"><span class="pre">socket.error</span></tt></a>.</p>
<p>Non-blocking mode is supported through <tt class="xref docutils literal"><span class="pre">setblocking()</span></tt>. A generalization of
this based on timeouts is supported through <tt class="xref docutils literal"><span class="pre">settimeout()</span></tt>.</p>
<p>The module <tt class="xref docutils literal"><span class="pre">socket</span></tt> exports the following constants and functions:</p>
<dl class="exception">
<dt id="socket.error">
<em class="property">exception </em><tt class="descclassname">socket.</tt><tt class="descname">error</tt><a class="headerlink" href="#socket.error" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-564">This exception is raised for socket-related errors. The accompanying value is
either a string telling what went wrong or a pair <tt class="docutils literal"><span class="pre">(errno,</span> <span class="pre">string)</span></tt>
representing an error returned by a system call, similar to the value
accompanying <a title="os.error" class="reference external" href="os.html#os.error"><tt class="xref docutils literal"><span class="pre">os.error</span></tt></a>. See the module <a title="Standard errno system symbols." class="reference external" href="errno.html#module-errno"><tt class="xref docutils literal"><span class="pre">errno</span></tt></a>, which contains names
for the error codes defined by the underlying operating system.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 2.6: </span><a title="socket.error" class="reference internal" href="#socket.error"><tt class="xref docutils literal"><span class="pre">socket.error</span></tt></a> is now a child class of <a title="exceptions.IOError" class="reference external" href="exceptions.html#exceptions.IOError"><tt class="xref docutils literal"><span class="pre">IOError</span></tt></a>.</p>
</dd></dl>
<dl class="exception">
<dt id="socket.herror">
<em class="property">exception </em><tt class="descclassname">socket.</tt><tt class="descname">herror</tt><a class="headerlink" href="#socket.herror" title="Permalink to this definition">¶</a></dt>
<dd><p>This exception is raised for address-related errors, i.e. for functions that use
<em>h_errno</em> in the C API, including <a title="socket.gethostbyname_ex" class="reference internal" href="#socket.gethostbyname_ex"><tt class="xref docutils literal"><span class="pre">gethostbyname_ex()</span></tt></a> and
<a title="socket.gethostbyaddr" class="reference internal" href="#socket.gethostbyaddr"><tt class="xref docutils literal"><span class="pre">gethostbyaddr()</span></tt></a>.</p>
<p>The accompanying value is a pair <tt class="docutils literal"><span class="pre">(h_errno,</span> <span class="pre">string)</span></tt> representing an error
returned by a library call. <em>string</em> represents the description of <em>h_errno</em>, as
returned by the <tt class="xref docutils literal"><span class="pre">hstrerror()</span></tt> C function.</p>
</dd></dl>
<dl class="exception">
<dt id="socket.gaierror">
<em class="property">exception </em><tt class="descclassname">socket.</tt><tt class="descname">gaierror</tt><a class="headerlink" href="#socket.gaierror" title="Permalink to this definition">¶</a></dt>
<dd>This exception is raised for address-related errors, for <a title="socket.getaddrinfo" class="reference internal" href="#socket.getaddrinfo"><tt class="xref docutils literal"><span class="pre">getaddrinfo()</span></tt></a> and
<a title="socket.getnameinfo" class="reference internal" href="#socket.getnameinfo"><tt class="xref docutils literal"><span class="pre">getnameinfo()</span></tt></a>. The accompanying value is a pair <tt class="docutils literal"><span class="pre">(error,</span> <span class="pre">string)</span></tt>
representing an error returned by a library call. <em>string</em> represents the
description of <em>error</em>, as returned by the <tt class="xref docutils literal"><span class="pre">gai_strerror()</span></tt> C function. The
<em>error</em> value will match one of the <tt class="xref docutils literal"><span class="pre">EAI_*</span></tt> constants defined in this
module.</dd></dl>
<dl class="exception">
<dt id="socket.timeout">
<em class="property">exception </em><tt class="descclassname">socket.</tt><tt class="descname">timeout</tt><a class="headerlink" href="#socket.timeout" title="Permalink to this definition">¶</a></dt>
<dd><p>This exception is raised when a timeout occurs on a socket which has had
timeouts enabled via a prior call to <tt class="xref docutils literal"><span class="pre">settimeout()</span></tt>. The accompanying value
is a string whose value is currently always “timed out”.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="data">
<dt id="socket.AF_UNIX">
<tt class="descclassname">socket.</tt><tt class="descname">AF_UNIX</tt><a class="headerlink" href="#socket.AF_UNIX" title="Permalink to this definition">¶</a></dt>
<dt id="socket.AF_INET">
<tt class="descclassname">socket.</tt><tt class="descname">AF_INET</tt><a class="headerlink" href="#socket.AF_INET" title="Permalink to this definition">¶</a></dt>
<dt id="socket.AF_INET6">
<tt class="descclassname">socket.</tt><tt class="descname">AF_INET6</tt><a class="headerlink" href="#socket.AF_INET6" title="Permalink to this definition">¶</a></dt>
<dd>These constants represent the address (and protocol) families, used for the
first argument to <a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a>. If the <a title="socket.AF_UNIX" class="reference internal" href="#socket.AF_UNIX"><tt class="xref docutils literal"><span class="pre">AF_UNIX</span></tt></a> constant is not
defined then this protocol is unsupported.</dd></dl>
<dl class="data">
<dt id="socket.SOCK_STREAM">
<tt class="descclassname">socket.</tt><tt class="descname">SOCK_STREAM</tt><a class="headerlink" href="#socket.SOCK_STREAM" title="Permalink to this definition">¶</a></dt>
<dt id="socket.SOCK_DGRAM">
<tt class="descclassname">socket.</tt><tt class="descname">SOCK_DGRAM</tt><a class="headerlink" href="#socket.SOCK_DGRAM" title="Permalink to this definition">¶</a></dt>
<dt id="socket.SOCK_RAW">
<tt class="descclassname">socket.</tt><tt class="descname">SOCK_RAW</tt><a class="headerlink" href="#socket.SOCK_RAW" title="Permalink to this definition">¶</a></dt>
<dt id="socket.SOCK_RDM">
<tt class="descclassname">socket.</tt><tt class="descname">SOCK_RDM</tt><a class="headerlink" href="#socket.SOCK_RDM" title="Permalink to this definition">¶</a></dt>
<dt id="socket.SOCK_SEQPACKET">
<tt class="descclassname">socket.</tt><tt class="descname">SOCK_SEQPACKET</tt><a class="headerlink" href="#socket.SOCK_SEQPACKET" title="Permalink to this definition">¶</a></dt>
<dd>These constants represent the socket types, used for the second argument to
<a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a>. (Only <a title="socket.SOCK_STREAM" class="reference internal" href="#socket.SOCK_STREAM"><tt class="xref docutils literal"><span class="pre">SOCK_STREAM</span></tt></a> and <a title="socket.SOCK_DGRAM" class="reference internal" href="#socket.SOCK_DGRAM"><tt class="xref docutils literal"><span class="pre">SOCK_DGRAM</span></tt></a> appear to be
generally useful.)</dd></dl>
<dl class="data">
<dt>
<tt class="descname">SO_*</tt></dt>
<dt id="socket.SOMAXCONN">
<tt class="descclassname">socket.</tt><tt class="descname">SOMAXCONN</tt><a class="headerlink" href="#socket.SOMAXCONN" title="Permalink to this definition">¶</a></dt>
<dt>
<tt class="descname">MSG_*</tt></dt>
<dt>
<tt class="descname">SOL_*</tt></dt>
<dt>
<tt class="descname">IPPROTO_*</tt></dt>
<dt>
<tt class="descname">IPPORT_*</tt></dt>
<dt>
<tt class="descname">INADDR_*</tt></dt>
<dt>
<tt class="descname">IP_*</tt></dt>
<dt>
<tt class="descname">IPV6_*</tt></dt>
<dt>
<tt class="descname">EAI_*</tt></dt>
<dt>
<tt class="descname">AI_*</tt></dt>
<dt>
<tt class="descname">NI_*</tt></dt>
<dt>
<tt class="descname">TCP_*</tt></dt>
<dd>Many constants of these forms, documented in the Unix documentation on sockets
and/or the IP protocol, are also defined in the socket module. They are
generally used in arguments to the <tt class="xref docutils literal"><span class="pre">setsockopt()</span></tt> and <tt class="xref docutils literal"><span class="pre">getsockopt()</span></tt>
methods of socket objects. In most cases, only those symbols that are defined
in the Unix header files are defined; for a few symbols, default values are
provided.</dd></dl>
<dl class="data">
<dt>
<tt class="descname">SIO_*</tt></dt>
<dt>
<tt class="descname">RCVALL_*</tt></dt>
<dd><p>Constants for Windows’ WSAIoctl(). The constants are used as arguments to the
<tt class="xref docutils literal"><span class="pre">ioctl()</span></tt> method of socket objects.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="data">
<dt>
<tt class="descname">TIPC_*</tt></dt>
<dd><p>TIPC related constants, matching the ones exported by the C socket API. See
the TIPC documentation for more information.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="data">
<dt id="socket.has_ipv6">
<tt class="descclassname">socket.</tt><tt class="descname">has_ipv6</tt><a class="headerlink" href="#socket.has_ipv6" title="Permalink to this definition">¶</a></dt>
<dd><p>This constant contains a boolean value which indicates if IPv6 is supported on
this platform.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.create_connection">
<tt class="descclassname">socket.</tt><tt class="descname">create_connection</tt><big>(</big><em>address</em><span class="optional">[</span>, <em>timeout</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.create_connection" title="Permalink to this definition">¶</a></dt>
<dd><p>Convenience function. Connect to <em>address</em> (a 2-tuple <tt class="docutils literal"><span class="pre">(host,</span> <span class="pre">port)</span></tt>),
and return the socket object. Passing the optional <em>timeout</em> parameter will
set the timeout on the socket instance before attempting to connect. If no
<em>timeout</em> is supplied, the global default timeout setting returned by
<a title="socket.getdefaulttimeout" class="reference internal" href="#socket.getdefaulttimeout"><tt class="xref docutils literal"><span class="pre">getdefaulttimeout()</span></tt></a> is used.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.getaddrinfo">
<tt class="descclassname">socket.</tt><tt class="descname">getaddrinfo</tt><big>(</big><em>host</em>, <em>port</em><span class="optional">[</span>, <em>family</em><span class="optional">[</span>, <em>socktype</em><span class="optional">[</span>, <em>proto</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.getaddrinfo" title="Permalink to this definition">¶</a></dt>
<dd><p>Resolves the <em>host</em>/<em>port</em> argument, into a sequence of 5-tuples that contain
all the necessary arguments for creating the corresponding socket. <em>host</em> is a domain
name, a string representation of an IPv4/v6 address or <tt class="xref docutils literal"><span class="pre">None</span></tt>. <em>port</em> is a string
service name such as <tt class="docutils literal"><span class="pre">'http'</span></tt>, a numeric port number or <tt class="xref docutils literal"><span class="pre">None</span></tt>.
The rest of the arguments are optional and must be numeric if specified.
By passing <tt class="xref docutils literal"><span class="pre">None</span></tt> as the value of <em>host</em> and <em>port</em>, , you can pass <tt class="docutils literal"><span class="pre">NULL</span></tt> to the C API.</p>
<p>The <a title="socket.getaddrinfo" class="reference internal" href="#socket.getaddrinfo"><tt class="xref docutils literal"><span class="pre">getaddrinfo()</span></tt></a> function returns a list of 5-tuples with the following
structure:</p>
<p><tt class="docutils literal"><span class="pre">(family,</span> <span class="pre">socktype,</span> <span class="pre">proto,</span> <span class="pre">canonname,</span> <span class="pre">sockaddr)</span></tt></p>
<p><em>family</em>, <em>socktype</em>, <em>proto</em> are all integers and are meant to be passed to the
<a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a> function. <em>canonname</em> is a string representing the canonical name
of the <em>host</em>. It can be a numeric IPv4/v6 address when <tt class="xref docutils literal"><span class="pre">AI_CANONNAME</span></tt> is
specified for a numeric <em>host</em>. <em>sockaddr</em> is a tuple describing a socket
address, as described above. See the source for <tt class="xref docutils literal"><span class="pre">socket</span></tt> and other
library modules for a typical usage of the function.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.getfqdn">
<tt class="descclassname">socket.</tt><tt class="descname">getfqdn</tt><big>(</big><span class="optional">[</span><em>name</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.getfqdn" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a fully qualified domain name for <em>name</em>. If <em>name</em> is omitted or empty,
it is interpreted as the local host. To find the fully qualified name, the
hostname returned by <a title="socket.gethostbyaddr" class="reference internal" href="#socket.gethostbyaddr"><tt class="xref docutils literal"><span class="pre">gethostbyaddr()</span></tt></a> is checked, followed by aliases for the
host, if available. The first name which includes a period is selected. In
case no fully qualified domain name is available, the hostname as returned by
<a title="socket.gethostname" class="reference internal" href="#socket.gethostname"><tt class="xref docutils literal"><span class="pre">gethostname()</span></tt></a> is returned.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.0.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.gethostbyname">
<tt class="descclassname">socket.</tt><tt class="descname">gethostbyname</tt><big>(</big><em>hostname</em><big>)</big><a class="headerlink" href="#socket.gethostbyname" title="Permalink to this definition">¶</a></dt>
<dd>Translate a host name to IPv4 address format. The IPv4 address is returned as a
string, such as <tt class="docutils literal"><span class="pre">'100.50.200.5'</span></tt>. If the host name is an IPv4 address itself
it is returned unchanged. See <a title="socket.gethostbyname_ex" class="reference internal" href="#socket.gethostbyname_ex"><tt class="xref docutils literal"><span class="pre">gethostbyname_ex()</span></tt></a> for a more complete
interface. <a title="socket.gethostbyname" class="reference internal" href="#socket.gethostbyname"><tt class="xref docutils literal"><span class="pre">gethostbyname()</span></tt></a> does not support IPv6 name resolution, and
<a title="socket.getaddrinfo" class="reference internal" href="#socket.getaddrinfo"><tt class="xref docutils literal"><span class="pre">getaddrinfo()</span></tt></a> should be used instead for IPv4/v6 dual stack support.</dd></dl>
<dl class="function">
<dt id="socket.gethostbyname_ex">
<tt class="descclassname">socket.</tt><tt class="descname">gethostbyname_ex</tt><big>(</big><em>hostname</em><big>)</big><a class="headerlink" href="#socket.gethostbyname_ex" title="Permalink to this definition">¶</a></dt>
<dd>Translate a host name to IPv4 address format, extended interface. Return a
triple <tt class="docutils literal"><span class="pre">(hostname,</span> <span class="pre">aliaslist,</span> <span class="pre">ipaddrlist)</span></tt> where <em>hostname</em> is the primary
host name responding to the given <em>ip_address</em>, <em>aliaslist</em> is a (possibly
empty) list of alternative host names for the same address, and <em>ipaddrlist</em> is
a list of IPv4 addresses for the same interface on the same host (often but not
always a single address). <a title="socket.gethostbyname_ex" class="reference internal" href="#socket.gethostbyname_ex"><tt class="xref docutils literal"><span class="pre">gethostbyname_ex()</span></tt></a> does not support IPv6 name
resolution, and <a title="socket.getaddrinfo" class="reference internal" href="#socket.getaddrinfo"><tt class="xref docutils literal"><span class="pre">getaddrinfo()</span></tt></a> should be used instead for IPv4/v6 dual
stack support.</dd></dl>
<dl class="function">
<dt id="socket.gethostname">
<tt class="descclassname">socket.</tt><tt class="descname">gethostname</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.gethostname" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a string containing the hostname of the machine where the Python
interpreter is currently executing.</p>
<p>If you want to know the current machine’s IP address, you may want to use
<tt class="docutils literal"><span class="pre">gethostbyname(gethostname())</span></tt>. This operation assumes that there is a
valid address-to-host mapping for the host, and the assumption does not
always hold.</p>
<p>Note: <a title="socket.gethostname" class="reference internal" href="#socket.gethostname"><tt class="xref docutils literal"><span class="pre">gethostname()</span></tt></a> doesn’t always return the fully qualified domain
name; use <tt class="docutils literal"><span class="pre">getfqdn()</span></tt> (see above).</p>
</dd></dl>
<dl class="function">
<dt id="socket.gethostbyaddr">
<tt class="descclassname">socket.</tt><tt class="descname">gethostbyaddr</tt><big>(</big><em>ip_address</em><big>)</big><a class="headerlink" href="#socket.gethostbyaddr" title="Permalink to this definition">¶</a></dt>
<dd>Return a triple <tt class="docutils literal"><span class="pre">(hostname,</span> <span class="pre">aliaslist,</span> <span class="pre">ipaddrlist)</span></tt> where <em>hostname</em> is the
primary host name responding to the given <em>ip_address</em>, <em>aliaslist</em> is a
(possibly empty) list of alternative host names for the same address, and
<em>ipaddrlist</em> is a list of IPv4/v6 addresses for the same interface on the same
host (most likely containing only a single address). To find the fully qualified
domain name, use the function <a title="socket.getfqdn" class="reference internal" href="#socket.getfqdn"><tt class="xref docutils literal"><span class="pre">getfqdn()</span></tt></a>. <a title="socket.gethostbyaddr" class="reference internal" href="#socket.gethostbyaddr"><tt class="xref docutils literal"><span class="pre">gethostbyaddr()</span></tt></a> supports
both IPv4 and IPv6.</dd></dl>
<dl class="function">
<dt id="socket.getnameinfo">
<tt class="descclassname">socket.</tt><tt class="descname">getnameinfo</tt><big>(</big><em>sockaddr</em>, <em>flags</em><big>)</big><a class="headerlink" href="#socket.getnameinfo" title="Permalink to this definition">¶</a></dt>
<dd><p>Translate a socket address <em>sockaddr</em> into a 2-tuple <tt class="docutils literal"><span class="pre">(host,</span> <span class="pre">port)</span></tt>. Depending
on the settings of <em>flags</em>, the result can contain a fully-qualified domain name
or numeric address representation in <em>host</em>. Similarly, <em>port</em> can contain a
string port name or a numeric port number.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.getprotobyname">
<tt class="descclassname">socket.</tt><tt class="descname">getprotobyname</tt><big>(</big><em>protocolname</em><big>)</big><a class="headerlink" href="#socket.getprotobyname" title="Permalink to this definition">¶</a></dt>
<dd>Translate an Internet protocol name (for example, <tt class="docutils literal"><span class="pre">'icmp'</span></tt>) to a constant
suitable for passing as the (optional) third argument to the <a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a>
function. This is usually only needed for sockets opened in “raw” mode
(<a title="socket.SOCK_RAW" class="reference internal" href="#socket.SOCK_RAW"><tt class="xref docutils literal"><span class="pre">SOCK_RAW</span></tt></a>); for the normal socket modes, the correct protocol is chosen
automatically if the protocol is omitted or zero.</dd></dl>
<dl class="function">
<dt id="socket.getservbyname">
<tt class="descclassname">socket.</tt><tt class="descname">getservbyname</tt><big>(</big><em>servicename</em><span class="optional">[</span>, <em>protocolname</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.getservbyname" title="Permalink to this definition">¶</a></dt>
<dd>Translate an Internet service name and protocol name to a port number for that
service. The optional protocol name, if given, should be <tt class="docutils literal"><span class="pre">'tcp'</span></tt> or
<tt class="docutils literal"><span class="pre">'udp'</span></tt>, otherwise any protocol will match.</dd></dl>
<dl class="function">
<dt id="socket.getservbyport">
<tt class="descclassname">socket.</tt><tt class="descname">getservbyport</tt><big>(</big><em>port</em><span class="optional">[</span>, <em>protocolname</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.getservbyport" title="Permalink to this definition">¶</a></dt>
<dd>Translate an Internet port number and protocol name to a service name for that
service. The optional protocol name, if given, should be <tt class="docutils literal"><span class="pre">'tcp'</span></tt> or
<tt class="docutils literal"><span class="pre">'udp'</span></tt>, otherwise any protocol will match.</dd></dl>
<dl class="function">
<dt id="socket.socket">
<tt class="descclassname">socket.</tt><tt class="descname">socket</tt><big>(</big><span class="optional">[</span><em>family</em><span class="optional">[</span>, <em>type</em><span class="optional">[</span>, <em>proto</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket" title="Permalink to this definition">¶</a></dt>
<dd>Create a new socket using the given address family, socket type and protocol
number. The address family should be <a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a> (the default),
<a title="socket.AF_INET6" class="reference internal" href="#socket.AF_INET6"><tt class="xref docutils literal"><span class="pre">AF_INET6</span></tt></a> or <a title="socket.AF_UNIX" class="reference internal" href="#socket.AF_UNIX"><tt class="xref docutils literal"><span class="pre">AF_UNIX</span></tt></a>. The socket type should be
<a title="socket.SOCK_STREAM" class="reference internal" href="#socket.SOCK_STREAM"><tt class="xref docutils literal"><span class="pre">SOCK_STREAM</span></tt></a> (the default), <a title="socket.SOCK_DGRAM" class="reference internal" href="#socket.SOCK_DGRAM"><tt class="xref docutils literal"><span class="pre">SOCK_DGRAM</span></tt></a> or perhaps one of the
other <tt class="docutils literal"><span class="pre">SOCK_</span></tt> constants. The protocol number is usually zero and may be
omitted in that case.</dd></dl>
<dl class="function">
<dt id="socket.socketpair">
<tt class="descclassname">socket.</tt><tt class="descname">socketpair</tt><big>(</big><span class="optional">[</span><em>family</em><span class="optional">[</span>, <em>type</em><span class="optional">[</span>, <em>proto</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socketpair" title="Permalink to this definition">¶</a></dt>
<dd><p>Build a pair of connected socket objects using the given address family, socket
type, and protocol number. Address family, socket type, and protocol number are
as for the <a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a> function above. The default family is <a title="socket.AF_UNIX" class="reference internal" href="#socket.AF_UNIX"><tt class="xref docutils literal"><span class="pre">AF_UNIX</span></tt></a>
if defined on the platform; otherwise, the default is <a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a>.
Availability: Unix.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.4.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.fromfd">
<tt class="descclassname">socket.</tt><tt class="descname">fromfd</tt><big>(</big><em>fd</em>, <em>family</em>, <em>type</em><span class="optional">[</span>, <em>proto</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.fromfd" title="Permalink to this definition">¶</a></dt>
<dd>Duplicate the file descriptor <em>fd</em> (an integer as returned by a file object’s
<tt class="xref docutils literal"><span class="pre">fileno()</span></tt> method) and build a socket object from the result. Address
family, socket type and protocol number are as for the <a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a> function
above. The file descriptor should refer to a socket, but this is not checked —
subsequent operations on the object may fail if the file descriptor is invalid.
This function is rarely needed, but can be used to get or set socket options on
a socket passed to a program as standard input or output (such as a server
started by the Unix inet daemon). The socket is assumed to be in blocking mode.
Availability: Unix.</dd></dl>
<dl class="function">
<dt id="socket.ntohl">
<tt class="descclassname">socket.</tt><tt class="descname">ntohl</tt><big>(</big><em>x</em><big>)</big><a class="headerlink" href="#socket.ntohl" title="Permalink to this definition">¶</a></dt>
<dd>Convert 32-bit positive integers from network to host byte order. On machines
where the host byte order is the same as network byte order, this is a no-op;
otherwise, it performs a 4-byte swap operation.</dd></dl>
<dl class="function">
<dt id="socket.ntohs">
<tt class="descclassname">socket.</tt><tt class="descname">ntohs</tt><big>(</big><em>x</em><big>)</big><a class="headerlink" href="#socket.ntohs" title="Permalink to this definition">¶</a></dt>
<dd>Convert 16-bit positive integers from network to host byte order. On machines
where the host byte order is the same as network byte order, this is a no-op;
otherwise, it performs a 2-byte swap operation.</dd></dl>
<dl class="function">
<dt id="socket.htonl">
<tt class="descclassname">socket.</tt><tt class="descname">htonl</tt><big>(</big><em>x</em><big>)</big><a class="headerlink" href="#socket.htonl" title="Permalink to this definition">¶</a></dt>
<dd>Convert 32-bit positive integers from host to network byte order. On machines
where the host byte order is the same as network byte order, this is a no-op;
otherwise, it performs a 4-byte swap operation.</dd></dl>
<dl class="function">
<dt id="socket.htons">
<tt class="descclassname">socket.</tt><tt class="descname">htons</tt><big>(</big><em>x</em><big>)</big><a class="headerlink" href="#socket.htons" title="Permalink to this definition">¶</a></dt>
<dd>Convert 16-bit positive integers from host to network byte order. On machines
where the host byte order is the same as network byte order, this is a no-op;
otherwise, it performs a 2-byte swap operation.</dd></dl>
<dl class="function">
<dt id="socket.inet_aton">
<tt class="descclassname">socket.</tt><tt class="descname">inet_aton</tt><big>(</big><em>ip_string</em><big>)</big><a class="headerlink" href="#socket.inet_aton" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert an IPv4 address from dotted-quad string format (for example,
‘123.45.67.89’) to 32-bit packed binary format, as a string four characters in
length. This is useful when conversing with a program that uses the standard C
library and needs objects of type <tt class="xref docutils literal"><span class="pre">struct</span> <span class="pre">in_addr</span></tt>, which is the C type
for the 32-bit packed binary this function returns.</p>
<p><a title="socket.inet_aton" class="reference internal" href="#socket.inet_aton"><tt class="xref docutils literal"><span class="pre">inet_aton()</span></tt></a> also accepts strings with less than three dots; see the
Unix manual page <em>inet(3)</em> for details.</p>
<p>If the IPv4 address string passed to this function is invalid,
<a title="socket.error" class="reference internal" href="#socket.error"><tt class="xref docutils literal"><span class="pre">socket.error</span></tt></a> will be raised. Note that exactly what is valid depends on
the underlying C implementation of <tt class="xref docutils literal"><span class="pre">inet_aton()</span></tt>.</p>
<p><a title="socket.inet_aton" class="reference internal" href="#socket.inet_aton"><tt class="xref docutils literal"><span class="pre">inet_aton()</span></tt></a> does not support IPv6, and <a title="socket.inet_pton" class="reference internal" href="#socket.inet_pton"><tt class="xref docutils literal"><span class="pre">inet_pton()</span></tt></a> should be used
instead for IPv4/v6 dual stack support.</p>
</dd></dl>
<dl class="function">
<dt id="socket.inet_ntoa">
<tt class="descclassname">socket.</tt><tt class="descname">inet_ntoa</tt><big>(</big><em>packed_ip</em><big>)</big><a class="headerlink" href="#socket.inet_ntoa" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a 32-bit packed IPv4 address (a string four characters in length) to its
standard dotted-quad string representation (for example, ‘123.45.67.89’). This
is useful when conversing with a program that uses the standard C library and
needs objects of type <tt class="xref docutils literal"><span class="pre">struct</span> <span class="pre">in_addr</span></tt>, which is the C type for the
32-bit packed binary data this function takes as an argument.</p>
<p>If the string passed to this function is not exactly 4 bytes in length,
<a title="socket.error" class="reference internal" href="#socket.error"><tt class="xref docutils literal"><span class="pre">socket.error</span></tt></a> will be raised. <a title="socket.inet_ntoa" class="reference internal" href="#socket.inet_ntoa"><tt class="xref docutils literal"><span class="pre">inet_ntoa()</span></tt></a> does not support IPv6, and
<a title="socket.inet_ntop" class="reference internal" href="#socket.inet_ntop"><tt class="xref docutils literal"><span class="pre">inet_ntop()</span></tt></a> should be used instead for IPv4/v6 dual stack support.</p>
</dd></dl>
<dl class="function">
<dt id="socket.inet_pton">
<tt class="descclassname">socket.</tt><tt class="descname">inet_pton</tt><big>(</big><em>address_family</em>, <em>ip_string</em><big>)</big><a class="headerlink" href="#socket.inet_pton" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert an IP address from its family-specific string format to a packed, binary
format. <a title="socket.inet_pton" class="reference internal" href="#socket.inet_pton"><tt class="xref docutils literal"><span class="pre">inet_pton()</span></tt></a> is useful when a library or network protocol calls for
an object of type <tt class="xref docutils literal"><span class="pre">struct</span> <span class="pre">in_addr</span></tt> (similar to <a title="socket.inet_aton" class="reference internal" href="#socket.inet_aton"><tt class="xref docutils literal"><span class="pre">inet_aton()</span></tt></a>) or
<tt class="xref docutils literal"><span class="pre">struct</span> <span class="pre">in6_addr</span></tt>.</p>
<p>Supported values for <em>address_family</em> are currently <a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a> and
<a title="socket.AF_INET6" class="reference internal" href="#socket.AF_INET6"><tt class="xref docutils literal"><span class="pre">AF_INET6</span></tt></a>. If the IP address string <em>ip_string</em> is invalid,
<a title="socket.error" class="reference internal" href="#socket.error"><tt class="xref docutils literal"><span class="pre">socket.error</span></tt></a> will be raised. Note that exactly what is valid depends on
both the value of <em>address_family</em> and the underlying implementation of
<tt class="xref docutils literal"><span class="pre">inet_pton()</span></tt>.</p>
<p>Availability: Unix (maybe not all platforms).</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.inet_ntop">
<tt class="descclassname">socket.</tt><tt class="descname">inet_ntop</tt><big>(</big><em>address_family</em>, <em>packed_ip</em><big>)</big><a class="headerlink" href="#socket.inet_ntop" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a packed IP address (a string of some number of characters) to its
standard, family-specific string representation (for example, <tt class="docutils literal"><span class="pre">'7.10.0.5'</span></tt> or
<tt class="docutils literal"><span class="pre">'5aef:2b::8'</span></tt>) <a title="socket.inet_ntop" class="reference internal" href="#socket.inet_ntop"><tt class="xref docutils literal"><span class="pre">inet_ntop()</span></tt></a> is useful when a library or network protocol
returns an object of type <tt class="xref docutils literal"><span class="pre">struct</span> <span class="pre">in_addr</span></tt> (similar to <a title="socket.inet_ntoa" class="reference internal" href="#socket.inet_ntoa"><tt class="xref docutils literal"><span class="pre">inet_ntoa()</span></tt></a>)
or <tt class="xref docutils literal"><span class="pre">struct</span> <span class="pre">in6_addr</span></tt>.</p>
<p>Supported values for <em>address_family</em> are currently <a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a> and
<a title="socket.AF_INET6" class="reference internal" href="#socket.AF_INET6"><tt class="xref docutils literal"><span class="pre">AF_INET6</span></tt></a>. If the string <em>packed_ip</em> is not the correct length for the
specified address family, <a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref docutils literal"><span class="pre">ValueError</span></tt></a> will be raised. A
<a title="socket.error" class="reference internal" href="#socket.error"><tt class="xref docutils literal"><span class="pre">socket.error</span></tt></a> is raised for errors from the call to <a title="socket.inet_ntop" class="reference internal" href="#socket.inet_ntop"><tt class="xref docutils literal"><span class="pre">inet_ntop()</span></tt></a>.</p>
<p>Availability: Unix (maybe not all platforms).</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.getdefaulttimeout">
<tt class="descclassname">socket.</tt><tt class="descname">getdefaulttimeout</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.getdefaulttimeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the default timeout in floating seconds for new socket objects. A value
of <tt class="xref docutils literal"><span class="pre">None</span></tt> indicates that new socket objects have no timeout. When the socket
module is first imported, the default is <tt class="xref docutils literal"><span class="pre">None</span></tt>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="function">
<dt id="socket.setdefaulttimeout">
<tt class="descclassname">socket.</tt><tt class="descname">setdefaulttimeout</tt><big>(</big><em>timeout</em><big>)</big><a class="headerlink" href="#socket.setdefaulttimeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the default timeout in floating seconds for new socket objects. A value of
<tt class="xref docutils literal"><span class="pre">None</span></tt> indicates that new socket objects have no timeout. When the socket
module is first imported, the default is <tt class="xref docutils literal"><span class="pre">None</span></tt>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="data">
<dt id="socket.SocketType">
<tt class="descclassname">socket.</tt><tt class="descname">SocketType</tt><a class="headerlink" href="#socket.SocketType" title="Permalink to this definition">¶</a></dt>
<dd>This is a Python type object that represents the socket object type. It is the
same as <tt class="docutils literal"><span class="pre">type(socket(...))</span></tt>.</dd></dl>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>Module <a title="A framework for network servers." class="reference external" href="socketserver.html#module-SocketServer"><tt class="xref docutils literal"><span class="pre">SocketServer</span></tt></a></dt>
<dd>Classes that simplify writing network servers.</dd>
</dl>
</div>
<div class="section" id="socket-objects">
<span id="id1"></span><h2>18.2.1. Socket Objects<a class="headerlink" href="#socket-objects" title="Permalink to this headline">¶</a></h2>
<p>Socket objects have the following methods. Except for <tt class="xref docutils literal"><span class="pre">makefile()</span></tt> these
correspond to Unix system calls applicable to sockets.</p>
<dl class="method">
<dt id="socket.socket.accept">
<tt class="descclassname">socket.</tt><tt class="descname">accept</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.socket.accept" title="Permalink to this definition">¶</a></dt>
<dd>Accept a connection. The socket must be bound to an address and listening for
connections. The return value is a pair <tt class="docutils literal"><span class="pre">(conn,</span> <span class="pre">address)</span></tt> where <em>conn</em> is a
<em>new</em> socket object usable to send and receive data on the connection, and
<em>address</em> is the address bound to the socket on the other end of the connection.</dd></dl>
<dl class="method">
<dt id="socket.socket.bind">
<tt class="descclassname">socket.</tt><tt class="descname">bind</tt><big>(</big><em>address</em><big>)</big><a class="headerlink" href="#socket.socket.bind" title="Permalink to this definition">¶</a></dt>
<dd><p>Bind the socket to <em>address</em>. The socket must not already be bound. (The format
of <em>address</em> depends on the address family — see above.)</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This method has historically accepted a pair of parameters for <a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a>
addresses instead of only a tuple. This was never intentional and is no longer
available in Python 2.0 and later.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="socket.socket.close">
<tt class="descclassname">socket.</tt><tt class="descname">close</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.socket.close" title="Permalink to this definition">¶</a></dt>
<dd>Close the socket. All future operations on the socket object will fail. The
remote end will receive no more data (after queued data is flushed). Sockets are
automatically closed when they are garbage-collected.</dd></dl>
<dl class="method">
<dt id="socket.socket.connect">
<tt class="descclassname">socket.</tt><tt class="descname">connect</tt><big>(</big><em>address</em><big>)</big><a class="headerlink" href="#socket.socket.connect" title="Permalink to this definition">¶</a></dt>
<dd><p>Connect to a remote socket at <em>address</em>. (The format of <em>address</em> depends on the
address family — see above.)</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This method has historically accepted a pair of parameters for <a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a>
addresses instead of only a tuple. This was never intentional and is no longer
available in Python 2.0 and later.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="socket.socket.connect_ex">
<tt class="descclassname">socket.</tt><tt class="descname">connect_ex</tt><big>(</big><em>address</em><big>)</big><a class="headerlink" href="#socket.socket.connect_ex" title="Permalink to this definition">¶</a></dt>
<dd><p>Like <tt class="docutils literal"><span class="pre">connect(address)</span></tt>, but return an error indicator instead of raising an
exception for errors returned by the C-level <tt class="xref docutils literal"><span class="pre">connect()</span></tt> call (other
problems, such as “host not found,” can still raise exceptions). The error
indicator is <tt class="docutils literal"><span class="pre">0</span></tt> if the operation succeeded, otherwise the value of the
<tt class="xref docutils literal"><span class="pre">errno</span></tt> variable. This is useful to support, for example, asynchronous
connects.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This method has historically accepted a pair of parameters for <a title="socket.AF_INET" class="reference internal" href="#socket.AF_INET"><tt class="xref docutils literal"><span class="pre">AF_INET</span></tt></a>
addresses instead of only a tuple. This was never intentional and is no longer
available in Python 2.0 and later.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="socket.socket.fileno">
<tt class="descclassname">socket.</tt><tt class="descname">fileno</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.socket.fileno" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the socket’s file descriptor (a small integer). This is useful with
<a title="select.select" class="reference external" href="select.html#select.select"><tt class="xref docutils literal"><span class="pre">select.select()</span></tt></a>.</p>
<p>Under Windows the small integer returned by this method cannot be used where a
file descriptor can be used (such as <a title="os.fdopen" class="reference external" href="os.html#os.fdopen"><tt class="xref docutils literal"><span class="pre">os.fdopen()</span></tt></a>). Unix does not have
this limitation.</p>
</dd></dl>
<dl class="method">
<dt id="socket.socket.getpeername">
<tt class="descclassname">socket.</tt><tt class="descname">getpeername</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.socket.getpeername" title="Permalink to this definition">¶</a></dt>
<dd>Return the remote address to which the socket is connected. This is useful to
find out the port number of a remote IPv4/v6 socket, for instance. (The format
of the address returned depends on the address family — see above.) On some
systems this function is not supported.</dd></dl>
<dl class="method">
<dt id="socket.socket.getsockname">
<tt class="descclassname">socket.</tt><tt class="descname">getsockname</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.socket.getsockname" title="Permalink to this definition">¶</a></dt>
<dd>Return the socket’s own address. This is useful to find out the port number of
an IPv4/v6 socket, for instance. (The format of the address returned depends on
the address family — see above.)</dd></dl>
<dl class="method">
<dt id="socket.socket.getsockopt">
<tt class="descclassname">socket.</tt><tt class="descname">getsockopt</tt><big>(</big><em>level</em>, <em>optname</em><span class="optional">[</span>, <em>buflen</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.getsockopt" title="Permalink to this definition">¶</a></dt>
<dd>Return the value of the given socket option (see the Unix man page
<em>getsockopt(2)</em>). The needed symbolic constants (<tt class="xref docutils literal"><span class="pre">SO_*</span></tt> etc.)
are defined in this module. If <em>buflen</em> is absent, an integer option is assumed
and its integer value is returned by the function. If <em>buflen</em> is present, it
specifies the maximum length of the buffer used to receive the option in, and
this buffer is returned as a string. It is up to the caller to decode the
contents of the buffer (see the optional built-in module <a title="Interpret strings as packed binary data." class="reference external" href="struct.html#module-struct"><tt class="xref docutils literal"><span class="pre">struct</span></tt></a> for a way
to decode C structures encoded as strings).</dd></dl>
<dl class="method">
<dt id="socket.socket.ioctl">
<tt class="descclassname">socket.</tt><tt class="descname">ioctl</tt><big>(</big><em>control</em>, <em>option</em><big>)</big><a class="headerlink" href="#socket.socket.ioctl" title="Permalink to this definition">¶</a></dt>
<dd><table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Platform:</th><td class="field-body">Windows</td>
</tr>
</tbody>
</table>
<p>The <a title="socket.socket.ioctl" class="reference internal" href="#socket.socket.ioctl"><tt class="xref docutils literal"><span class="pre">ioctl()</span></tt></a> method is a limited interface to the WSAIoctl system
interface. Please refer to the MSDN documentation for more information.</p>
<p>On other platforms, the generic <a title="fcntl.fcntl" class="reference external" href="fcntl.html#fcntl.fcntl"><tt class="xref docutils literal"><span class="pre">fcntl.fcntl()</span></tt></a> and <a title="fcntl.ioctl" class="reference external" href="fcntl.html#fcntl.ioctl"><tt class="xref docutils literal"><span class="pre">fcntl.ioctl()</span></tt></a>
functions may be used; they accept a socket object as their first argument.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.6.</span></p>
</dd></dl>
<dl class="method">
<dt id="socket.socket.listen">
<tt class="descclassname">socket.</tt><tt class="descname">listen</tt><big>(</big><em>backlog</em><big>)</big><a class="headerlink" href="#socket.socket.listen" title="Permalink to this definition">¶</a></dt>
<dd>Listen for connections made to the socket. The <em>backlog</em> argument specifies the
maximum number of queued connections and should be at least 1; the maximum value
is system-dependent (usually 5).</dd></dl>
<dl class="method">
<dt id="socket.socket.makefile">
<tt class="descclassname">socket.</tt><tt class="descname">makefile</tt><big>(</big><span class="optional">[</span><em>mode</em><span class="optional">[</span>, <em>bufsize</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.makefile" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-565">Return a <em>file object</em> associated with the socket. (File objects are
described in <a class="reference external" href="stdtypes.html#bltin-file-objects"><em>File Objects</em></a>.) The file object
references a <tt class="xref docutils literal"><span class="pre">dup()</span></tt>ped version of the socket file descriptor, so the
file object and socket object may be closed or garbage-collected independently.
The socket must be in blocking mode (it can not have a timeout). The optional
<em>mode</em> and <em>bufsize</em> arguments are interpreted the same way as by the built-in
<a title="file" class="reference external" href="functions.html#file"><tt class="xref docutils literal"><span class="pre">file()</span></tt></a> function.</p>
</dd></dl>
<dl class="method">
<dt id="socket.socket.recv">
<tt class="descclassname">socket.</tt><tt class="descname">recv</tt><big>(</big><em>bufsize</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.recv" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive data from the socket. The return value is a string representing the
data received. The maximum amount of data to be received at once is specified
by <em>bufsize</em>. See the Unix manual page <em>recv(2)</em> for the meaning of
the optional argument <em>flags</em>; it defaults to zero.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">For best match with hardware and network realities, the value of <em>bufsize</em>
should be a relatively small power of 2, for example, 4096.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="socket.socket.recvfrom">
<tt class="descclassname">socket.</tt><tt class="descname">recvfrom</tt><big>(</big><em>bufsize</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.recvfrom" title="Permalink to this definition">¶</a></dt>
<dd>Receive data from the socket. The return value is a pair <tt class="docutils literal"><span class="pre">(string,</span> <span class="pre">address)</span></tt>
where <em>string</em> is a string representing the data received and <em>address</em> is the
address of the socket sending the data. See the Unix manual page
<em>recv(2)</em> for the meaning of the optional argument <em>flags</em>; it defaults
to zero. (The format of <em>address</em> depends on the address family — see above.)</dd></dl>
<dl class="method">
<dt id="socket.socket.recvfrom_into">
<tt class="descclassname">socket.</tt><tt class="descname">recvfrom_into</tt><big>(</big><em>buffer</em><span class="optional">[</span>, <em>nbytes</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.recvfrom_into" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive data from the socket, writing it into <em>buffer</em> instead of creating a
new string. The return value is a pair <tt class="docutils literal"><span class="pre">(nbytes,</span> <span class="pre">address)</span></tt> where <em>nbytes</em> is
the number of bytes received and <em>address</em> is the address of the socket sending
the data. See the Unix manual page <em>recv(2)</em> for the meaning of the
optional argument <em>flags</em>; it defaults to zero. (The format of <em>address</em>
depends on the address family — see above.)</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
<dl class="method">
<dt id="socket.socket.recv_into">
<tt class="descclassname">socket.</tt><tt class="descname">recv_into</tt><big>(</big><em>buffer</em><span class="optional">[</span>, <em>nbytes</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.recv_into" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive up to <em>nbytes</em> bytes from the socket, storing the data into a buffer
rather than creating a new string. If <em>nbytes</em> is not specified (or 0),
receive up to the size available in the given buffer. See the Unix manual page
<em>recv(2)</em> for the meaning of the optional argument <em>flags</em>; it defaults
to zero.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
<dl class="method">
<dt id="socket.socket.send">
<tt class="descclassname">socket.</tt><tt class="descname">send</tt><big>(</big><em>string</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.send" title="Permalink to this definition">¶</a></dt>
<dd>Send data to the socket. The socket must be connected to a remote socket. The
optional <em>flags</em> argument has the same meaning as for <a title="socket.socket.recv" class="reference internal" href="#socket.socket.recv"><tt class="xref docutils literal"><span class="pre">recv()</span></tt></a> above.
Returns the number of bytes sent. Applications are responsible for checking that
all data has been sent; if only some of the data was transmitted, the
application needs to attempt delivery of the remaining data.</dd></dl>
<dl class="method">
<dt id="socket.socket.sendall">
<tt class="descclassname">socket.</tt><tt class="descname">sendall</tt><big>(</big><em>string</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#socket.socket.sendall" title="Permalink to this definition">¶</a></dt>
<dd>Send data to the socket. The socket must be connected to a remote socket. The
optional <em>flags</em> argument has the same meaning as for <a title="socket.socket.recv" class="reference internal" href="#socket.socket.recv"><tt class="xref docutils literal"><span class="pre">recv()</span></tt></a> above.
Unlike <a title="socket.socket.send" class="reference internal" href="#socket.socket.send"><tt class="xref docutils literal"><span class="pre">send()</span></tt></a>, this method continues to send data from <em>string</em> until
either all data has been sent or an error occurs. <tt class="xref docutils literal"><span class="pre">None</span></tt> is returned on
success. On error, an exception is raised, and there is no way to determine how
much data, if any, was successfully sent.</dd></dl>
<dl class="method">
<dt id="socket.socket.sendto">
<tt class="descclassname">socket.</tt><tt class="descname">sendto</tt><big>(</big><em>string</em><span class="optional">[</span>, <em>flags</em><span class="optional">]</span>, <em>address</em><big>)</big><a class="headerlink" href="#socket.socket.sendto" title="Permalink to this definition">¶</a></dt>
<dd>Send data to the socket. The socket should not be connected to a remote socket,
since the destination socket is specified by <em>address</em>. The optional <em>flags</em>
argument has the same meaning as for <a title="socket.socket.recv" class="reference internal" href="#socket.socket.recv"><tt class="xref docutils literal"><span class="pre">recv()</span></tt></a> above. Return the number of
bytes sent. (The format of <em>address</em> depends on the address family — see
above.)</dd></dl>
<dl class="method">
<dt id="socket.socket.setblocking">
<tt class="descclassname">socket.</tt><tt class="descname">setblocking</tt><big>(</big><em>flag</em><big>)</big><a class="headerlink" href="#socket.socket.setblocking" title="Permalink to this definition">¶</a></dt>
<dd>Set blocking or non-blocking mode of the socket: if <em>flag</em> is 0, the socket is
set to non-blocking, else to blocking mode. Initially all sockets are in
blocking mode. In non-blocking mode, if a <a title="socket.socket.recv" class="reference internal" href="#socket.socket.recv"><tt class="xref docutils literal"><span class="pre">recv()</span></tt></a> call doesn’t find any
data, or if a <a title="socket.socket.send" class="reference internal" href="#socket.socket.send"><tt class="xref docutils literal"><span class="pre">send()</span></tt></a> call can’t immediately dispose of the data, a
<a title="socket.error" class="reference internal" href="#socket.error"><tt class="xref docutils literal"><span class="pre">error</span></tt></a> exception is raised; in blocking mode, the calls block until they
can proceed. <tt class="docutils literal"><span class="pre">s.setblocking(0)</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">s.settimeout(0)</span></tt>;
<tt class="docutils literal"><span class="pre">s.setblocking(1)</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">s.settimeout(None)</span></tt>.</dd></dl>
<dl class="method">
<dt id="socket.socket.settimeout">
<tt class="descclassname">socket.</tt><tt class="descname">settimeout</tt><big>(</big><em>value</em><big>)</big><a class="headerlink" href="#socket.socket.settimeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Set a timeout on blocking socket operations. The <em>value</em> argument can be a
nonnegative float expressing seconds, or <tt class="xref docutils literal"><span class="pre">None</span></tt>. If a float is given,
subsequent socket operations will raise an <a title="socket.timeout" class="reference internal" href="#socket.timeout"><tt class="xref docutils literal"><span class="pre">timeout</span></tt></a> exception if the
timeout period <em>value</em> has elapsed before the operation has completed. Setting
a timeout of <tt class="xref docutils literal"><span class="pre">None</span></tt> disables timeouts on socket operations.
<tt class="docutils literal"><span class="pre">s.settimeout(0.0)</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">s.setblocking(0)</span></tt>;
<tt class="docutils literal"><span class="pre">s.settimeout(None)</span></tt> is equivalent to <tt class="docutils literal"><span class="pre">s.setblocking(1)</span></tt>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<dl class="method">
<dt id="socket.socket.gettimeout">
<tt class="descclassname">socket.</tt><tt class="descname">gettimeout</tt><big>(</big><big>)</big><a class="headerlink" href="#socket.socket.gettimeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the timeout in floating seconds associated with socket operations, or
<tt class="xref docutils literal"><span class="pre">None</span></tt> if no timeout is set. This reflects the last call to
<a title="socket.socket.setblocking" class="reference internal" href="#socket.socket.setblocking"><tt class="xref docutils literal"><span class="pre">setblocking()</span></tt></a> or <a title="socket.socket.settimeout" class="reference internal" href="#socket.socket.settimeout"><tt class="xref docutils literal"><span class="pre">settimeout()</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.3.</span></p>
</dd></dl>
<p>Some notes on socket blocking and timeouts: A socket object can be in one of
three modes: blocking, non-blocking, or timeout. Sockets are always created in
blocking mode. In blocking mode, operations block until complete or
the system returns an error (such as connection timed out). In
non-blocking mode, operations fail (with an error that is unfortunately
system-dependent) if they cannot be completed immediately. In timeout mode,
operations fail if they cannot be completed within the timeout specified for the
socket or if the system returns an error. The <tt class="xref docutils literal"><span class="pre">setblocking()</span></tt> method is simply
a shorthand for certain <tt class="xref docutils literal"><span class="pre">settimeout()</span></tt> calls.</p>
<p>Timeout mode internally sets the socket in non-blocking mode. The blocking and
timeout modes are shared between file descriptors and socket objects that refer
to the same network endpoint. A consequence of this is that file objects
returned by the <tt class="xref docutils literal"><span class="pre">makefile()</span></tt> method must only be used when the socket is in
blocking mode; in timeout or non-blocking mode file operations that cannot be
completed immediately will fail.</p>
<p>Note that the <tt class="xref docutils literal"><span class="pre">connect()</span></tt> operation is subject to the timeout setting, and
in general it is recommended to call <tt class="xref docutils literal"><span class="pre">settimeout()</span></tt> before calling
<tt class="xref docutils literal"><span class="pre">connect()</span></tt> or pass a timeout parameter to <a title="socket.create_connection" class="reference internal" href="#socket.create_connection"><tt class="xref docutils literal"><span class="pre">create_connection()</span></tt></a>.
The system network stack may return a connection timeout error
of its own regardless of any Python socket timeout setting.</p>
<dl class="method">
<dt id="socket.socket.setsockopt">
<tt class="descclassname">socket.</tt><tt class="descname">setsockopt</tt><big>(</big><em>level</em>, <em>optname</em>, <em>value</em><big>)</big><a class="headerlink" href="#socket.socket.setsockopt" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-566">Set the value of the given socket option (see the Unix manual page
<em>setsockopt(2)</em>). The needed symbolic constants are defined in the
<tt class="xref docutils literal"><span class="pre">socket</span></tt> module (<tt class="xref docutils literal"><span class="pre">SO_*</span></tt> etc.). The value can be an integer or a
string representing a buffer. In the latter case it is up to the caller to
ensure that the string contains the proper bits (see the optional built-in
module <a title="Interpret strings as packed binary data." class="reference external" href="struct.html#module-struct"><tt class="xref docutils literal"><span class="pre">struct</span></tt></a> for a way to encode C structures as strings).</p>
</dd></dl>
<dl class="method">
<dt id="socket.socket.shutdown">
<tt class="descclassname">socket.</tt><tt class="descname">shutdown</tt><big>(</big><em>how</em><big>)</big><a class="headerlink" href="#socket.socket.shutdown" title="Permalink to this definition">¶</a></dt>
<dd>Shut down one or both halves of the connection. If <em>how</em> is <tt class="xref docutils literal"><span class="pre">SHUT_RD</span></tt>,
further receives are disallowed. If <em>how</em> is <tt class="xref docutils literal"><span class="pre">SHUT_WR</span></tt>, further sends
are disallowed. If <em>how</em> is <tt class="xref docutils literal"><span class="pre">SHUT_RDWR</span></tt>, further sends and receives are
disallowed.</dd></dl>
<p>Note that there are no methods <tt class="xref docutils literal"><span class="pre">read()</span></tt> or <tt class="xref docutils literal"><span class="pre">write()</span></tt>; use <tt class="xref docutils literal"><span class="pre">recv()</span></tt>
and <tt class="xref docutils literal"><span class="pre">send()</span></tt> without <em>flags</em> argument instead.</p>
<p>Socket objects also have these (read-only) attributes that correspond to the
values given to the <a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket</span></tt></a> constructor.</p>
<dl class="attribute">
<dt id="socket.socket.family">
<tt class="descclassname">socket.</tt><tt class="descname">family</tt><a class="headerlink" href="#socket.socket.family" title="Permalink to this definition">¶</a></dt>
<dd><p>The socket family.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
<dl class="attribute">
<dt id="socket.socket.type">
<tt class="descclassname">socket.</tt><tt class="descname">type</tt><a class="headerlink" href="#socket.socket.type" title="Permalink to this definition">¶</a></dt>
<dd><p>The socket type.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
<dl class="attribute">
<dt id="socket.socket.proto">
<tt class="descclassname">socket.</tt><tt class="descname">proto</tt><a class="headerlink" href="#socket.socket.proto" title="Permalink to this definition">¶</a></dt>
<dd><p>The socket protocol.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.5.</span></p>
</dd></dl>
</div>
<div class="section" id="example">
<span id="socket-example"></span><h2>18.2.2. Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2>
<p>Here are four minimal example programs using the TCP/IP protocol: a server that
echoes all data that it receives back (servicing only one client), and a client
using it. Note that a server must perform the sequence <a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a>,
<tt class="xref docutils literal"><span class="pre">bind()</span></tt>, <tt class="xref docutils literal"><span class="pre">listen()</span></tt>, <tt class="xref docutils literal"><span class="pre">accept()</span></tt> (possibly repeating the
<tt class="xref docutils literal"><span class="pre">accept()</span></tt> to service more than one client), while a client only needs the
sequence <a title="socket.socket" class="reference internal" href="#socket.socket"><tt class="xref docutils literal"><span class="pre">socket()</span></tt></a>, <tt class="xref docutils literal"><span class="pre">connect()</span></tt>. Also note that the server does not
<tt class="xref docutils literal"><span class="pre">send()</span></tt>/<tt class="xref docutils literal"><span class="pre">recv()</span></tt> on the socket it is listening on but on the new
socket returned by <tt class="xref docutils literal"><span class="pre">accept()</span></tt>.</p>
<p>The first two examples support IPv4 only.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Echo server program</span>
<span class="kn">import</span> <span class="nn">socket</span>
<span class="n">HOST</span> <span class="o">=</span> <span class="s">''</span> <span class="c"># Symbolic name meaning all available interfaces</span>
<span class="n">PORT</span> <span class="o">=</span> <span class="mi">50007</span> <span class="c"># Arbitrary non-privileged port</span>
<span class="n">s</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">s</span><span class="o">.</span><span class="n">bind</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">s</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="n">conn</span><span class="p">,</span> <span class="n">addr</span> <span class="o">=</span> <span class="n">s</span><span class="o">.</span><span class="n">accept</span><span class="p">()</span>
<span class="k">print</span> <span class="s">'Connected by'</span><span class="p">,</span> <span class="n">addr</span>
<span class="k">while</span> <span class="mi">1</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">conn</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">if</span> <span class="ow">not</span> <span class="n">data</span><span class="p">:</span> <span class="k">break</span>
<span class="n">conn</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="n">conn</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Echo client program</span>
<span class="kn">import</span> <span class="nn">socket</span>
<span class="n">HOST</span> <span class="o">=</span> <span class="s">'daring.cwi.nl'</span> <span class="c"># The remote host</span>
<span class="n">PORT</span> <span class="o">=</span> <span class="mi">50007</span> <span class="c"># The same port as used by the server</span>
<span class="n">s</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">s</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">s</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="s">'Hello, world'</span><span class="p">)</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">s</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">s</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">print</span> <span class="s">'Received'</span><span class="p">,</span> <span class="nb">repr</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
</pre></div>
</div>
<p>The next two examples are identical to the above two, but support both IPv4 and
IPv6. The server side will listen to the first address family available (it
should listen to both instead). On most of IPv6-ready systems, IPv6 will take
precedence and the server may not accept IPv4 traffic. The client side will try
to connect to the all addresses returned as a result of the name resolution, and
sends traffic to the first one connected successfully.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Echo server program</span>
<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="o">=</span> <span class="bp">None</span> <span class="c"># Symbolic name meaning all available interfaces</span>
<span class="n">PORT</span> <span class="o">=</span> <span class="mi">50007</span> <span class="c"># Arbitrary non-privileged port</span>
<span class="n">s</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">for</span> <span class="n">res</span> <span class="ow">in</span> <span class="n">socket</span><span class="o">.</span><span class="n">getaddrinfo</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">socket</span><span class="o">.</span><span class="n">AF_UNSPEC</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="mi">0</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">AI_PASSIVE</span><span class="p">):</span>
<span class="n">af</span><span class="p">,</span> <span class="n">socktype</span><span class="p">,</span> <span class="n">proto</span><span class="p">,</span> <span class="n">canonname</span><span class="p">,</span> <span class="n">sa</span> <span class="o">=</span> <span class="n">res</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">s</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">af</span><span class="p">,</span> <span class="n">socktype</span><span class="p">,</span> <span class="n">proto</span><span class="p">)</span>
<span class="k">except</span> <span class="n">socket</span><span class="o">.</span><span class="n">error</span><span class="p">,</span> <span class="n">msg</span><span class="p">:</span>
<span class="n">s</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">continue</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">s</span><span class="o">.</span><span class="n">bind</span><span class="p">(</span><span class="n">sa</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="k">except</span> <span class="n">socket</span><span class="o">.</span><span class="n">error</span><span class="p">,</span> <span class="n">msg</span><span class="p">:</span>
<span class="n">s</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">s</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">continue</span>
<span class="k">break</span>
<span class="k">if</span> <span class="n">s</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'could not open socket'</span>
<span class="n">sys</span><span class="o">.</span><span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="n">conn</span><span class="p">,</span> <span class="n">addr</span> <span class="o">=</span> <span class="n">s</span><span class="o">.</span><span class="n">accept</span><span class="p">()</span>
<span class="k">print</span> <span class="s">'Connected by'</span><span class="p">,</span> <span class="n">addr</span>
<span class="k">while</span> <span class="mi">1</span><span class="p">:</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">conn</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">if</span> <span class="ow">not</span> <span class="n">data</span><span class="p">:</span> <span class="k">break</span>
<span class="n">conn</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="n">conn</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Echo client program</span>
<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="o">=</span> <span class="s">'daring.cwi.nl'</span> <span class="c"># The remote host</span>
<span class="n">PORT</span> <span class="o">=</span> <span class="mi">50007</span> <span class="c"># The same port as used by the server</span>
<span class="n">s</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">for</span> <span class="n">res</span> <span class="ow">in</span> <span class="n">socket</span><span class="o">.</span><span class="n">getaddrinfo</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">socket</span><span class="o">.</span><span class="n">AF_UNSPEC</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">af</span><span class="p">,</span> <span class="n">socktype</span><span class="p">,</span> <span class="n">proto</span><span class="p">,</span> <span class="n">canonname</span><span class="p">,</span> <span class="n">sa</span> <span class="o">=</span> <span class="n">res</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">s</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">af</span><span class="p">,</span> <span class="n">socktype</span><span class="p">,</span> <span class="n">proto</span><span class="p">)</span>
<span class="k">except</span> <span class="n">socket</span><span class="o">.</span><span class="n">error</span><span class="p">,</span> <span class="n">msg</span><span class="p">:</span>
<span class="n">s</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">continue</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">s</span><span class="o">.</span><span class="n">connect</span><span class="p">(</span><span class="n">sa</span><span class="p">)</span>
<span class="k">except</span> <span class="n">socket</span><span class="o">.</span><span class="n">error</span><span class="p">,</span> <span class="n">msg</span><span class="p">:</span>
<span class="n">s</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="n">s</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">continue</span>
<span class="k">break</span>
<span class="k">if</span> <span class="n">s</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'could not open socket'</span>
<span class="n">sys</span><span class="o">.</span><span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="s">'Hello, world'</span><span class="p">)</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">s</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">s</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">print</span> <span class="s">'Received'</span><span class="p">,</span> <span class="nb">repr</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
</pre></div>
</div>
<p>The last example shows how to write a very simple network sniffer with raw
sockets on Windows. The example requires administrator privileges to modify
the interface:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">socket</span>
<span class="c"># the public network interface</span>
<span class="n">HOST</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">gethostbyname</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">gethostname</span><span class="p">())</span>
<span class="c"># create a raw socket and bind it to the public interface</span>
<span class="n">s</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_RAW</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">IPPROTO_IP</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">bind</span><span class="p">((</span><span class="n">HOST</span><span class="p">,</span> <span class="mi">0</span><span class="p">))</span>
<span class="c"># Include IP headers</span>
<span class="n">s</span><span class="o">.</span><span class="n">setsockopt</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">IPPROTO_IP</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">IP_HDRINCL</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="c"># receive all packages</span>
<span class="n">s</span><span class="o">.</span><span class="n">ioctl</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">SIO_RCVALL</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">RCVALL_ON</span><span class="p">)</span>
<span class="c"># receive a package</span>
<span class="k">print</span> <span class="n">s</span><span class="o">.</span><span class="n">recvfrom</span><span class="p">(</span><span class="mi">65565</span><span class="p">)</span>
<span class="c"># disabled promiscuous mode</span>
<span class="n">s</span><span class="o">.</span><span class="n">ioctl</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">SIO_RCVALL</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">RCVALL_OFF</span><span class="p">)</span>
</pre></div>
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<li><a class="reference external" href="#">18.2. <tt class="docutils literal"><span class="pre">socket</span></tt> — Low-level networking interface</a><ul>
<li><a class="reference external" href="#socket-objects">18.2.1. Socket Objects</a></li>
<li><a class="reference external" href="#example">18.2.2. Example</a></li>
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