2 :mod:`socket` --- Low-level networking interface
3 ================================================
6 :synopsis: Low-level networking interface.
9 This module provides access to the BSD *socket* interface. It is available on
10 all modern Unix systems, Windows, Mac OS X, BeOS, OS/2, and probably additional
15 Some behavior may be platform dependent, since calls are made to the operating
18 For an introduction to socket programming (in C), see the following papers: An
19 Introductory 4.3BSD Interprocess Communication Tutorial, by Stuart Sechrest and
20 An Advanced 4.3BSD Interprocess Communication Tutorial, by Samuel J. Leffler et
21 al, both in the UNIX Programmer's Manual, Supplementary Documents 1 (sections
22 PS1:7 and PS1:8). The platform-specific reference material for the various
23 socket-related system calls are also a valuable source of information on the
24 details of socket semantics. For Unix, refer to the manual pages; for Windows,
25 see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may
26 want to refer to :rfc:`3493` titled Basic Socket Interface Extensions for IPv6.
28 .. index:: object: socket
30 The Python interface is a straightforward transliteration of the Unix system
31 call and library interface for sockets to Python's object-oriented style: the
32 :func:`socket` function returns a :dfn:`socket object` whose methods implement
33 the various socket system calls. Parameter types are somewhat higher-level than
34 in the C interface: as with :meth:`read` and :meth:`write` operations on Python
35 files, buffer allocation on receive operations is automatic, and buffer length
36 is implicit on send operations.
38 Socket addresses are represented as follows: A single string is used for the
39 :const:`AF_UNIX` address family. A pair ``(host, port)`` is used for the
40 :const:`AF_INET` address family, where *host* is a string representing either a
41 hostname in Internet domain notation like ``'daring.cwi.nl'`` or an IPv4 address
42 like ``'100.50.200.5'``, and *port* is an integral port number. For
43 :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo,
44 scopeid)`` is used, where *flowinfo* and *scopeid* represents ``sin6_flowinfo``
45 and ``sin6_scope_id`` member in :const:`struct sockaddr_in6` in C. For
46 :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for
47 backward compatibility. Note, however, omission of *scopeid* can cause problems
48 in manipulating scoped IPv6 addresses. Other address families are currently not
49 supported. The address format required by a particular socket object is
50 automatically selected based on the address family specified when the socket
53 For IPv4 addresses, two special forms are accepted instead of a host address:
54 the empty string represents :const:`INADDR_ANY`, and the string
55 ``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. The behavior is not
56 available for IPv6 for backward compatibility, therefore, you may want to avoid
57 these if you intend to support IPv6 with your Python programs.
59 If you use a hostname in the *host* portion of IPv4/v6 socket address, the
60 program may show a nondeterministic behavior, as Python uses the first address
61 returned from the DNS resolution. The socket address will be resolved
62 differently into an actual IPv4/v6 address, depending on the results from DNS
63 resolution and/or the host configuration. For deterministic behavior use a
64 numeric address in *host* portion.
67 AF_NETLINK sockets are represented as pairs ``pid, groups``.
70 Linux-only support for TIPC is also available using the :const:`AF_TIPC`
71 address family. TIPC is an open, non-IP based networked protocol designed
72 for use in clustered computer environments. Addresses are represented by a
73 tuple, and the fields depend on the address type. The general tuple form is
74 ``(addr_type, v1, v2, v3 [, scope])``, where:
76 - *addr_type* is one of TIPC_ADDR_NAMESEQ, TIPC_ADDR_NAME, or
78 - *scope* is one of TIPC_ZONE_SCOPE, TIPC_CLUSTER_SCOPE, and
80 - If *addr_type* is TIPC_ADDR_NAME, then *v1* is the server type, *v2* is
81 the port identifier, and *v3* should be 0.
83 If *addr_type* is TIPC_ADDR_NAMESEQ, then *v1* is the server type, *v2*
84 is the lower port number, and *v3* is the upper port number.
86 If *addr_type* is TIPC_ADDR_ID, then *v1* is the node, *v2* is the
87 reference, and *v3* should be set to 0.
90 All errors raise exceptions. The normal exceptions for invalid argument types
91 and out-of-memory conditions can be raised; errors related to socket or address
92 semantics raise the error :exc:`socket.error`.
94 Non-blocking mode is supported through :meth:`setblocking`. A generalization of
95 this based on timeouts is supported through :meth:`settimeout`.
97 The module :mod:`socket` exports the following constants and functions:
102 .. index:: module: errno
104 This exception is raised for socket-related errors. The accompanying value is
105 either a string telling what went wrong or a pair ``(errno, string)``
106 representing an error returned by a system call, similar to the value
107 accompanying :exc:`os.error`. See the module :mod:`errno`, which contains names
108 for the error codes defined by the underlying operating system.
110 .. versionchanged:: 2.6
111 :exc:`socket.error` is now a child class of :exc:`IOError`.
114 .. exception:: herror
116 This exception is raised for address-related errors, i.e. for functions that use
117 *h_errno* in the C API, including :func:`gethostbyname_ex` and
118 :func:`gethostbyaddr`.
120 The accompanying value is a pair ``(h_errno, string)`` representing an error
121 returned by a library call. *string* represents the description of *h_errno*, as
122 returned by the :cfunc:`hstrerror` C function.
125 .. exception:: gaierror
127 This exception is raised for address-related errors, for :func:`getaddrinfo` and
128 :func:`getnameinfo`. The accompanying value is a pair ``(error, string)``
129 representing an error returned by a library call. *string* represents the
130 description of *error*, as returned by the :cfunc:`gai_strerror` C function. The
131 *error* value will match one of the :const:`EAI_\*` constants defined in this
135 .. exception:: timeout
137 This exception is raised when a timeout occurs on a socket which has had
138 timeouts enabled via a prior call to :meth:`settimeout`. The accompanying value
139 is a string whose value is currently always "timed out".
141 .. versionadded:: 2.3
148 These constants represent the address (and protocol) families, used for the
149 first argument to :func:`socket`. If the :const:`AF_UNIX` constant is not
150 defined then this protocol is unsupported.
153 .. data:: SOCK_STREAM
159 These constants represent the socket types, used for the second argument to
160 :func:`socket`. (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be
178 Many constants of these forms, documented in the Unix documentation on sockets
179 and/or the IP protocol, are also defined in the socket module. They are
180 generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt`
181 methods of socket objects. In most cases, only those symbols that are defined
182 in the Unix header files are defined; for a few symbols, default values are
188 Constants for Windows' WSAIoctl(). The constants are used as arguments to the
189 :meth:`ioctl` method of socket objects.
191 .. versionadded:: 2.6
195 TIPC related constants, matching the ones exported by the C socket API. See
196 the TIPC documentation for more information.
198 .. versionadded:: 2.6
202 This constant contains a boolean value which indicates if IPv6 is supported on
205 .. versionadded:: 2.3
208 .. function:: create_connection(address[, timeout])
210 Convenience function. Connect to *address* (a 2-tuple ``(host, port)``),
211 and return the socket object. Passing the optional *timeout* parameter will
212 set the timeout on the socket instance before attempting to connect. If no
213 *timeout* is supplied, the global default timeout setting returned by
214 :func:`getdefaulttimeout` is used.
216 .. versionadded:: 2.6
219 .. function:: getaddrinfo(host, port[, family[, socktype[, proto[, flags]]]])
221 Resolves the *host*/*port* argument, into a sequence of 5-tuples that contain
222 all the necessary arguments for creating the corresponding socket. *host* is a domain
223 name, a string representation of an IPv4/v6 address or ``None``. *port* is a string
224 service name such as ``'http'``, a numeric port number or ``None``.
225 The rest of the arguments are optional and must be numeric if specified.
226 By passing ``None`` as the value of *host* and *port*, , you can pass ``NULL`` to the C API.
228 The :func:`getaddrinfo` function returns a list of 5-tuples with the following
231 ``(family, socktype, proto, canonname, sockaddr)``
233 *family*, *socktype*, *proto* are all integers and are meant to be passed to the
234 :func:`socket` function. *canonname* is a string representing the canonical name
235 of the *host*. It can be a numeric IPv4/v6 address when :const:`AI_CANONNAME` is
236 specified for a numeric *host*. *sockaddr* is a tuple describing a socket
237 address, as described above. See the source for :mod:`socket` and other
238 library modules for a typical usage of the function.
240 .. versionadded:: 2.2
243 .. function:: getfqdn([name])
245 Return a fully qualified domain name for *name*. If *name* is omitted or empty,
246 it is interpreted as the local host. To find the fully qualified name, the
247 hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the
248 host, if available. The first name which includes a period is selected. In
249 case no fully qualified domain name is available, the hostname as returned by
250 :func:`gethostname` is returned.
252 .. versionadded:: 2.0
255 .. function:: gethostbyname(hostname)
257 Translate a host name to IPv4 address format. The IPv4 address is returned as a
258 string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself
259 it is returned unchanged. See :func:`gethostbyname_ex` for a more complete
260 interface. :func:`gethostbyname` does not support IPv6 name resolution, and
261 :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support.
264 .. function:: gethostbyname_ex(hostname)
266 Translate a host name to IPv4 address format, extended interface. Return a
267 triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary
268 host name responding to the given *ip_address*, *aliaslist* is a (possibly
269 empty) list of alternative host names for the same address, and *ipaddrlist* is
270 a list of IPv4 addresses for the same interface on the same host (often but not
271 always a single address). :func:`gethostbyname_ex` does not support IPv6 name
272 resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual
276 .. function:: gethostname()
278 Return a string containing the hostname of the machine where the Python
279 interpreter is currently executing.
281 If you want to know the current machine's IP address, you may want to use
282 ``gethostbyname(gethostname())``. This operation assumes that there is a
283 valid address-to-host mapping for the host, and the assumption does not
286 Note: :func:`gethostname` doesn't always return the fully qualified domain
287 name; use ``getfqdn()`` (see above).
290 .. function:: gethostbyaddr(ip_address)
292 Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the
293 primary host name responding to the given *ip_address*, *aliaslist* is a
294 (possibly empty) list of alternative host names for the same address, and
295 *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same
296 host (most likely containing only a single address). To find the fully qualified
297 domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports
301 .. function:: getnameinfo(sockaddr, flags)
303 Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending
304 on the settings of *flags*, the result can contain a fully-qualified domain name
305 or numeric address representation in *host*. Similarly, *port* can contain a
306 string port name or a numeric port number.
308 .. versionadded:: 2.2
311 .. function:: getprotobyname(protocolname)
313 Translate an Internet protocol name (for example, ``'icmp'``) to a constant
314 suitable for passing as the (optional) third argument to the :func:`socket`
315 function. This is usually only needed for sockets opened in "raw" mode
316 (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen
317 automatically if the protocol is omitted or zero.
320 .. function:: getservbyname(servicename[, protocolname])
322 Translate an Internet service name and protocol name to a port number for that
323 service. The optional protocol name, if given, should be ``'tcp'`` or
324 ``'udp'``, otherwise any protocol will match.
327 .. function:: getservbyport(port[, protocolname])
329 Translate an Internet port number and protocol name to a service name for that
330 service. The optional protocol name, if given, should be ``'tcp'`` or
331 ``'udp'``, otherwise any protocol will match.
334 .. function:: socket([family[, type[, proto]]])
336 Create a new socket using the given address family, socket type and protocol
337 number. The address family should be :const:`AF_INET` (the default),
338 :const:`AF_INET6` or :const:`AF_UNIX`. The socket type should be
339 :const:`SOCK_STREAM` (the default), :const:`SOCK_DGRAM` or perhaps one of the
340 other ``SOCK_`` constants. The protocol number is usually zero and may be
341 omitted in that case.
344 .. function:: socketpair([family[, type[, proto]]])
346 Build a pair of connected socket objects using the given address family, socket
347 type, and protocol number. Address family, socket type, and protocol number are
348 as for the :func:`socket` function above. The default family is :const:`AF_UNIX`
349 if defined on the platform; otherwise, the default is :const:`AF_INET`.
352 .. versionadded:: 2.4
355 .. function:: fromfd(fd, family, type[, proto])
357 Duplicate the file descriptor *fd* (an integer as returned by a file object's
358 :meth:`fileno` method) and build a socket object from the result. Address
359 family, socket type and protocol number are as for the :func:`socket` function
360 above. The file descriptor should refer to a socket, but this is not checked ---
361 subsequent operations on the object may fail if the file descriptor is invalid.
362 This function is rarely needed, but can be used to get or set socket options on
363 a socket passed to a program as standard input or output (such as a server
364 started by the Unix inet daemon). The socket is assumed to be in blocking mode.
368 .. function:: ntohl(x)
370 Convert 32-bit positive integers from network to host byte order. On machines
371 where the host byte order is the same as network byte order, this is a no-op;
372 otherwise, it performs a 4-byte swap operation.
375 .. function:: ntohs(x)
377 Convert 16-bit positive integers from network to host byte order. On machines
378 where the host byte order is the same as network byte order, this is a no-op;
379 otherwise, it performs a 2-byte swap operation.
382 .. function:: htonl(x)
384 Convert 32-bit positive integers from host to network byte order. On machines
385 where the host byte order is the same as network byte order, this is a no-op;
386 otherwise, it performs a 4-byte swap operation.
389 .. function:: htons(x)
391 Convert 16-bit positive integers from host to network byte order. On machines
392 where the host byte order is the same as network byte order, this is a no-op;
393 otherwise, it performs a 2-byte swap operation.
396 .. function:: inet_aton(ip_string)
398 Convert an IPv4 address from dotted-quad string format (for example,
399 '123.45.67.89') to 32-bit packed binary format, as a string four characters in
400 length. This is useful when conversing with a program that uses the standard C
401 library and needs objects of type :ctype:`struct in_addr`, which is the C type
402 for the 32-bit packed binary this function returns.
404 If the IPv4 address string passed to this function is invalid,
405 :exc:`socket.error` will be raised. Note that exactly what is valid depends on
406 the underlying C implementation of :cfunc:`inet_aton`.
408 :func:`inet_aton` does not support IPv6, and :func:`getnameinfo` should be used
409 instead for IPv4/v6 dual stack support.
412 .. function:: inet_ntoa(packed_ip)
414 Convert a 32-bit packed IPv4 address (a string four characters in length) to its
415 standard dotted-quad string representation (for example, '123.45.67.89'). This
416 is useful when conversing with a program that uses the standard C library and
417 needs objects of type :ctype:`struct in_addr`, which is the C type for the
418 32-bit packed binary data this function takes as an argument.
420 If the string passed to this function is not exactly 4 bytes in length,
421 :exc:`socket.error` will be raised. :func:`inet_ntoa` does not support IPv6, and
422 :func:`getnameinfo` should be used instead for IPv4/v6 dual stack support.
425 .. function:: inet_pton(address_family, ip_string)
427 Convert an IP address from its family-specific string format to a packed, binary
428 format. :func:`inet_pton` is useful when a library or network protocol calls for
429 an object of type :ctype:`struct in_addr` (similar to :func:`inet_aton`) or
430 :ctype:`struct in6_addr`.
432 Supported values for *address_family* are currently :const:`AF_INET` and
433 :const:`AF_INET6`. If the IP address string *ip_string* is invalid,
434 :exc:`socket.error` will be raised. Note that exactly what is valid depends on
435 both the value of *address_family* and the underlying implementation of
438 Availability: Unix (maybe not all platforms).
440 .. versionadded:: 2.3
443 .. function:: inet_ntop(address_family, packed_ip)
445 Convert a packed IP address (a string of some number of characters) to its
446 standard, family-specific string representation (for example, ``'7.10.0.5'`` or
447 ``'5aef:2b::8'``) :func:`inet_ntop` is useful when a library or network protocol
448 returns an object of type :ctype:`struct in_addr` (similar to :func:`inet_ntoa`)
449 or :ctype:`struct in6_addr`.
451 Supported values for *address_family* are currently :const:`AF_INET` and
452 :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the
453 specified address family, :exc:`ValueError` will be raised. A
454 :exc:`socket.error` is raised for errors from the call to :func:`inet_ntop`.
456 Availability: Unix (maybe not all platforms).
458 .. versionadded:: 2.3
461 .. function:: getdefaulttimeout()
463 Return the default timeout in floating seconds for new socket objects. A value
464 of ``None`` indicates that new socket objects have no timeout. When the socket
465 module is first imported, the default is ``None``.
467 .. versionadded:: 2.3
470 .. function:: setdefaulttimeout(timeout)
472 Set the default timeout in floating seconds for new socket objects. A value of
473 ``None`` indicates that new socket objects have no timeout. When the socket
474 module is first imported, the default is ``None``.
476 .. versionadded:: 2.3
481 This is a Python type object that represents the socket object type. It is the
482 same as ``type(socket(...))``.
487 Module :mod:`SocketServer`
488 Classes that simplify writing network servers.
496 Socket objects have the following methods. Except for :meth:`makefile` these
497 correspond to Unix system calls applicable to sockets.
500 .. method:: socket.accept()
502 Accept a connection. The socket must be bound to an address and listening for
503 connections. The return value is a pair ``(conn, address)`` where *conn* is a
504 *new* socket object usable to send and receive data on the connection, and
505 *address* is the address bound to the socket on the other end of the connection.
508 .. method:: socket.bind(address)
510 Bind the socket to *address*. The socket must not already be bound. (The format
511 of *address* depends on the address family --- see above.)
515 This method has historically accepted a pair of parameters for :const:`AF_INET`
516 addresses instead of only a tuple. This was never intentional and is no longer
517 available in Python 2.0 and later.
520 .. method:: socket.close()
522 Close the socket. All future operations on the socket object will fail. The
523 remote end will receive no more data (after queued data is flushed). Sockets are
524 automatically closed when they are garbage-collected.
527 .. method:: socket.connect(address)
529 Connect to a remote socket at *address*. (The format of *address* depends on the
530 address family --- see above.)
534 This method has historically accepted a pair of parameters for :const:`AF_INET`
535 addresses instead of only a tuple. This was never intentional and is no longer
536 available in Python 2.0 and later.
539 .. method:: socket.connect_ex(address)
541 Like ``connect(address)``, but return an error indicator instead of raising an
542 exception for errors returned by the C-level :cfunc:`connect` call (other
543 problems, such as "host not found," can still raise exceptions). The error
544 indicator is ``0`` if the operation succeeded, otherwise the value of the
545 :cdata:`errno` variable. This is useful to support, for example, asynchronous
550 This method has historically accepted a pair of parameters for :const:`AF_INET`
551 addresses instead of only a tuple. This was never intentional and is no longer
552 available in Python 2.0 and later.
555 .. method:: socket.fileno()
557 Return the socket's file descriptor (a small integer). This is useful with
558 :func:`select.select`.
560 Under Windows the small integer returned by this method cannot be used where a
561 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have
565 .. method:: socket.getpeername()
567 Return the remote address to which the socket is connected. This is useful to
568 find out the port number of a remote IPv4/v6 socket, for instance. (The format
569 of the address returned depends on the address family --- see above.) On some
570 systems this function is not supported.
573 .. method:: socket.getsockname()
575 Return the socket's own address. This is useful to find out the port number of
576 an IPv4/v6 socket, for instance. (The format of the address returned depends on
577 the address family --- see above.)
580 .. method:: socket.getsockopt(level, optname[, buflen])
582 Return the value of the given socket option (see the Unix man page
583 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.)
584 are defined in this module. If *buflen* is absent, an integer option is assumed
585 and its integer value is returned by the function. If *buflen* is present, it
586 specifies the maximum length of the buffer used to receive the option in, and
587 this buffer is returned as a string. It is up to the caller to decode the
588 contents of the buffer (see the optional built-in module :mod:`struct` for a way
589 to decode C structures encoded as strings).
592 .. method:: socket.ioctl(control, option)
596 The :meth:`ioctl` method is a limited interface to the WSAIoctl system
597 interface. Please refer to the MSDN documentation for more information.
599 .. versionadded:: 2.6
602 .. method:: socket.listen(backlog)
604 Listen for connections made to the socket. The *backlog* argument specifies the
605 maximum number of queued connections and should be at least 1; the maximum value
606 is system-dependent (usually 5).
609 .. method:: socket.makefile([mode[, bufsize]])
611 .. index:: single: I/O control; buffering
613 Return a :dfn:`file object` associated with the socket. (File objects are
614 described in :ref:`bltin-file-objects`.) The file object
615 references a :cfunc:`dup`\ ped version of the socket file descriptor, so the
616 file object and socket object may be closed or garbage-collected independently.
617 The socket must be in blocking mode (it can not have a timeout). The optional
618 *mode* and *bufsize* arguments are interpreted the same way as by the built-in
619 :func:`file` function.
622 .. method:: socket.recv(bufsize[, flags])
624 Receive data from the socket. The return value is a string representing the
625 data received. The maximum amount of data to be received at once is specified
626 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of
627 the optional argument *flags*; it defaults to zero.
631 For best match with hardware and network realities, the value of *bufsize*
632 should be a relatively small power of 2, for example, 4096.
635 .. method:: socket.recvfrom(bufsize[, flags])
637 Receive data from the socket. The return value is a pair ``(string, address)``
638 where *string* is a string representing the data received and *address* is the
639 address of the socket sending the data. See the Unix manual page
640 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
641 to zero. (The format of *address* depends on the address family --- see above.)
644 .. method:: socket.recvfrom_into(buffer[, nbytes[, flags]])
646 Receive data from the socket, writing it into *buffer* instead of creating a
647 new string. The return value is a pair ``(nbytes, address)`` where *nbytes* is
648 the number of bytes received and *address* is the address of the socket sending
649 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the
650 optional argument *flags*; it defaults to zero. (The format of *address*
651 depends on the address family --- see above.)
653 .. versionadded:: 2.5
656 .. method:: socket.recv_into(buffer[, nbytes[, flags]])
658 Receive up to *nbytes* bytes from the socket, storing the data into a buffer
659 rather than creating a new string. If *nbytes* is not specified (or 0),
660 receive up to the size available in the given buffer. See the Unix manual page
661 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
664 .. versionadded:: 2.5
667 .. method:: socket.send(string[, flags])
669 Send data to the socket. The socket must be connected to a remote socket. The
670 optional *flags* argument has the same meaning as for :meth:`recv` above.
671 Returns the number of bytes sent. Applications are responsible for checking that
672 all data has been sent; if only some of the data was transmitted, the
673 application needs to attempt delivery of the remaining data.
676 .. method:: socket.sendall(string[, flags])
678 Send data to the socket. The socket must be connected to a remote socket. The
679 optional *flags* argument has the same meaning as for :meth:`recv` above.
680 Unlike :meth:`send`, this method continues to send data from *string* until
681 either all data has been sent or an error occurs. ``None`` is returned on
682 success. On error, an exception is raised, and there is no way to determine how
683 much data, if any, was successfully sent.
686 .. method:: socket.sendto(string[, flags], address)
688 Send data to the socket. The socket should not be connected to a remote socket,
689 since the destination socket is specified by *address*. The optional *flags*
690 argument has the same meaning as for :meth:`recv` above. Return the number of
691 bytes sent. (The format of *address* depends on the address family --- see
695 .. method:: socket.setblocking(flag)
697 Set blocking or non-blocking mode of the socket: if *flag* is 0, the socket is
698 set to non-blocking, else to blocking mode. Initially all sockets are in
699 blocking mode. In non-blocking mode, if a :meth:`recv` call doesn't find any
700 data, or if a :meth:`send` call can't immediately dispose of the data, a
701 :exc:`error` exception is raised; in blocking mode, the calls block until they
702 can proceed. ``s.setblocking(0)`` is equivalent to ``s.settimeout(0)``;
703 ``s.setblocking(1)`` is equivalent to ``s.settimeout(None)``.
706 .. method:: socket.settimeout(value)
708 Set a timeout on blocking socket operations. The *value* argument can be a
709 nonnegative float expressing seconds, or ``None``. If a float is given,
710 subsequent socket operations will raise an :exc:`timeout` exception if the
711 timeout period *value* has elapsed before the operation has completed. Setting
712 a timeout of ``None`` disables timeouts on socket operations.
713 ``s.settimeout(0.0)`` is equivalent to ``s.setblocking(0)``;
714 ``s.settimeout(None)`` is equivalent to ``s.setblocking(1)``.
716 .. versionadded:: 2.3
719 .. method:: socket.gettimeout()
721 Return the timeout in floating seconds associated with socket operations, or
722 ``None`` if no timeout is set. This reflects the last call to
723 :meth:`setblocking` or :meth:`settimeout`.
725 .. versionadded:: 2.3
727 Some notes on socket blocking and timeouts: A socket object can be in one of
728 three modes: blocking, non-blocking, or timeout. Sockets are always created in
729 blocking mode. In blocking mode, operations block until complete or
730 the system returns an error (such as connection timed out). In
731 non-blocking mode, operations fail (with an error that is unfortunately
732 system-dependent) if they cannot be completed immediately. In timeout mode,
733 operations fail if they cannot be completed within the timeout specified for the
734 socket or if the system returns an error. The :meth:`setblocking` method is simply
735 a shorthand for certain :meth:`settimeout` calls.
737 Timeout mode internally sets the socket in non-blocking mode. The blocking and
738 timeout modes are shared between file descriptors and socket objects that refer
739 to the same network endpoint. A consequence of this is that file objects
740 returned by the :meth:`makefile` method must only be used when the socket is in
741 blocking mode; in timeout or non-blocking mode file operations that cannot be
742 completed immediately will fail.
744 Note that the :meth:`connect` operation is subject to the timeout setting, and
745 in general it is recommended to call :meth:`settimeout` before calling
746 :meth:`connect` or pass a timeout parameter to :meth:`create_connection`.
747 The system network stack may return a connection timeout error
748 of its own regardless of any python socket timeout setting.
751 .. method:: socket.setsockopt(level, optname, value)
753 .. index:: module: struct
755 Set the value of the given socket option (see the Unix manual page
756 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the
757 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a
758 string representing a buffer. In the latter case it is up to the caller to
759 ensure that the string contains the proper bits (see the optional built-in
760 module :mod:`struct` for a way to encode C structures as strings).
763 .. method:: socket.shutdown(how)
765 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`,
766 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends
767 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are
770 Note that there are no methods :meth:`read` or :meth:`write`; use :meth:`recv`
771 and :meth:`send` without *flags* argument instead.
773 Socket objects also have these (read-only) attributes that correspond to the
774 values given to the :class:`socket` constructor.
777 .. attribute:: socket.family
781 .. versionadded:: 2.5
784 .. attribute:: socket.type
788 .. versionadded:: 2.5
791 .. attribute:: socket.proto
795 .. versionadded:: 2.5
803 Here are four minimal example programs using the TCP/IP protocol: a server that
804 echoes all data that it receives back (servicing only one client), and a client
805 using it. Note that a server must perform the sequence :func:`socket`,
806 :meth:`bind`, :meth:`listen`, :meth:`accept` (possibly repeating the
807 :meth:`accept` to service more than one client), while a client only needs the
808 sequence :func:`socket`, :meth:`connect`. Also note that the server does not
809 :meth:`send`/:meth:`recv` on the socket it is listening on but on the new
810 socket returned by :meth:`accept`.
812 The first two examples support IPv4 only. ::
814 # Echo server program
817 HOST = '' # Symbolic name meaning all available interfaces
818 PORT = 50007 # Arbitrary non-privileged port
819 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
822 conn, addr = s.accept()
823 print 'Connected by', addr
825 data = conn.recv(1024)
832 # Echo client program
835 HOST = 'daring.cwi.nl' # The remote host
836 PORT = 50007 # The same port as used by the server
837 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
838 s.connect((HOST, PORT))
839 s.send('Hello, world')
842 print 'Received', repr(data)
844 The next two examples are identical to the above two, but support both IPv4 and
845 IPv6. The server side will listen to the first address family available (it
846 should listen to both instead). On most of IPv6-ready systems, IPv6 will take
847 precedence and the server may not accept IPv4 traffic. The client side will try
848 to connect to the all addresses returned as a result of the name resolution, and
849 sends traffic to the first one connected successfully. ::
851 # Echo server program
855 HOST = None # Symbolic name meaning all available interfaces
856 PORT = 50007 # Arbitrary non-privileged port
858 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC,
859 socket.SOCK_STREAM, 0, socket.AI_PASSIVE):
860 af, socktype, proto, canonname, sa = res
862 s = socket.socket(af, socktype, proto)
863 except socket.error, msg:
869 except socket.error, msg:
875 print 'could not open socket'
877 conn, addr = s.accept()
878 print 'Connected by', addr
880 data = conn.recv(1024)
887 # Echo client program
891 HOST = 'daring.cwi.nl' # The remote host
892 PORT = 50007 # The same port as used by the server
894 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
895 af, socktype, proto, canonname, sa = res
897 s = socket.socket(af, socktype, proto)
898 except socket.error, msg:
903 except socket.error, msg:
909 print 'could not open socket'
911 s.send('Hello, world')
914 print 'Received', repr(data)
917 The last example shows how to write a very simple network sniffer with raw
918 sockets on Windows. The example requires administrator privileges to modify
923 # the public network interface
924 HOST = socket.gethostbyname(socket.gethostname())
926 # create a raw socket and bind it to the public interface
927 s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP)
931 s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
933 # receive all packages
934 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
937 print s.recvfrom(65565)
939 # disabled promiscuous mode
940 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)