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:`2553` 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 Connects to the *address* received (as usual, a ``(host, port)`` pair), with an
211 optional timeout for the connection. Especially useful for higher-level
212 protocols, it is not normally used directly from application-level code.
213 Passing the optional *timeout* parameter will set the timeout on the socket
214 instance (if it is not given or ``None``, the global default timeout setting is
217 .. versionadded:: 2.6
220 .. function:: getaddrinfo(host, port[, family[, socktype[, proto[, flags]]]])
222 Resolves the *host*/*port* argument, into a sequence of 5-tuples that contain
223 all the necessary argument for the sockets manipulation. *host* is a domain
224 name, a string representation of IPv4/v6 address or ``None``. *port* is a string
225 service name (like ``'http'``), a numeric port number or ``None``.
227 The rest of the arguments are optional and must be numeric if specified. For
228 *host* and *port*, by passing either an empty string or ``None``, you can pass
229 ``NULL`` to the C API. The :func:`getaddrinfo` function returns a list of
230 5-tuples with the following structure:
232 ``(family, socktype, proto, canonname, sockaddr)``
234 *family*, *socktype*, *proto* are all integer and are meant to be passed to the
235 :func:`socket` function. *canonname* is a string representing the canonical name
236 of the *host*. It can be a numeric IPv4/v6 address when :const:`AI_CANONNAME` is
237 specified for a numeric *host*. *sockaddr* is a tuple describing a socket
238 address, as described above. See the source for :mod:`socket` and other
239 library modules for a typical usage of the function.
241 .. versionadded:: 2.2
244 .. function:: getfqdn([name])
246 Return a fully qualified domain name for *name*. If *name* is omitted or empty,
247 it is interpreted as the local host. To find the fully qualified name, the
248 hostname returned by :func:`gethostbyaddr` is checked, then aliases for the
249 host, if available. The first name which includes a period is selected. In
250 case no fully qualified domain name is available, the hostname as returned by
251 :func:`gethostname` is returned.
253 .. versionadded:: 2.0
256 .. function:: gethostbyname(hostname)
258 Translate a host name to IPv4 address format. The IPv4 address is returned as a
259 string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself
260 it is returned unchanged. See :func:`gethostbyname_ex` for a more complete
261 interface. :func:`gethostbyname` does not support IPv6 name resolution, and
262 :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support.
265 .. function:: gethostbyname_ex(hostname)
267 Translate a host name to IPv4 address format, extended interface. Return a
268 triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary
269 host name responding to the given *ip_address*, *aliaslist* is a (possibly
270 empty) list of alternative host names for the same address, and *ipaddrlist* is
271 a list of IPv4 addresses for the same interface on the same host (often but not
272 always a single address). :func:`gethostbyname_ex` does not support IPv6 name
273 resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual
277 .. function:: gethostname()
279 Return a string containing the hostname of the machine where the Python
280 interpreter is currently executing. If you want to know the current machine's IP
281 address, you may want to use ``gethostbyname(gethostname())``. This operation
282 assumes that there is a valid address-to-host mapping for the host, and the
283 assumption does not always hold. Note: :func:`gethostname` doesn't always return
284 the fully qualified domain name; use ``getfqdn()`` (see above).
287 .. function:: gethostbyaddr(ip_address)
289 Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the
290 primary host name responding to the given *ip_address*, *aliaslist* is a
291 (possibly empty) list of alternative host names for the same address, and
292 *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same
293 host (most likely containing only a single address). To find the fully qualified
294 domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports
298 .. function:: getnameinfo(sockaddr, flags)
300 Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending
301 on the settings of *flags*, the result can contain a fully-qualified domain name
302 or numeric address representation in *host*. Similarly, *port* can contain a
303 string port name or a numeric port number.
305 .. versionadded:: 2.2
308 .. function:: getprotobyname(protocolname)
310 Translate an Internet protocol name (for example, ``'icmp'``) to a constant
311 suitable for passing as the (optional) third argument to the :func:`socket`
312 function. This is usually only needed for sockets opened in "raw" mode
313 (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen
314 automatically if the protocol is omitted or zero.
317 .. function:: getservbyname(servicename[, protocolname])
319 Translate an Internet service name and protocol name to a port number for that
320 service. The optional protocol name, if given, should be ``'tcp'`` or
321 ``'udp'``, otherwise any protocol will match.
324 .. function:: getservbyport(port[, protocolname])
326 Translate an Internet port number and protocol name to a service name for that
327 service. The optional protocol name, if given, should be ``'tcp'`` or
328 ``'udp'``, otherwise any protocol will match.
331 .. function:: socket([family[, type[, proto]]])
333 Create a new socket using the given address family, socket type and protocol
334 number. The address family should be :const:`AF_INET` (the default),
335 :const:`AF_INET6` or :const:`AF_UNIX`. The socket type should be
336 :const:`SOCK_STREAM` (the default), :const:`SOCK_DGRAM` or perhaps one of the
337 other ``SOCK_`` constants. The protocol number is usually zero and may be
338 omitted in that case.
341 .. function:: socketpair([family[, type[, proto]]])
343 Build a pair of connected socket objects using the given address family, socket
344 type, and protocol number. Address family, socket type, and protocol number are
345 as for the :func:`socket` function above. The default family is :const:`AF_UNIX`
346 if defined on the platform; otherwise, the default is :const:`AF_INET`.
349 .. versionadded:: 2.4
352 .. function:: fromfd(fd, family, type[, proto])
354 Duplicate the file descriptor *fd* (an integer as returned by a file object's
355 :meth:`fileno` method) and build a socket object from the result. Address
356 family, socket type and protocol number are as for the :func:`socket` function
357 above. The file descriptor should refer to a socket, but this is not checked ---
358 subsequent operations on the object may fail if the file descriptor is invalid.
359 This function is rarely needed, but can be used to get or set socket options on
360 a socket passed to a program as standard input or output (such as a server
361 started by the Unix inet daemon). The socket is assumed to be in blocking mode.
365 .. function:: ntohl(x)
367 Convert 32-bit positive integers from network to host byte order. On machines
368 where the host byte order is the same as network byte order, this is a no-op;
369 otherwise, it performs a 4-byte swap operation.
372 .. function:: ntohs(x)
374 Convert 16-bit positive integers from network to host byte order. On machines
375 where the host byte order is the same as network byte order, this is a no-op;
376 otherwise, it performs a 2-byte swap operation.
379 .. function:: htonl(x)
381 Convert 32-bit positive integers from host to network byte order. On machines
382 where the host byte order is the same as network byte order, this is a no-op;
383 otherwise, it performs a 4-byte swap operation.
386 .. function:: htons(x)
388 Convert 16-bit positive integers from host to network byte order. On machines
389 where the host byte order is the same as network byte order, this is a no-op;
390 otherwise, it performs a 2-byte swap operation.
393 .. function:: inet_aton(ip_string)
395 Convert an IPv4 address from dotted-quad string format (for example,
396 '123.45.67.89') to 32-bit packed binary format, as a string four characters in
397 length. This is useful when conversing with a program that uses the standard C
398 library and needs objects of type :ctype:`struct in_addr`, which is the C type
399 for the 32-bit packed binary this function returns.
401 If the IPv4 address string passed to this function is invalid,
402 :exc:`socket.error` will be raised. Note that exactly what is valid depends on
403 the underlying C implementation of :cfunc:`inet_aton`.
405 :func:`inet_aton` does not support IPv6, and :func:`getnameinfo` should be used
406 instead for IPv4/v6 dual stack support.
409 .. function:: inet_ntoa(packed_ip)
411 Convert a 32-bit packed IPv4 address (a string four characters in length) to its
412 standard dotted-quad string representation (for example, '123.45.67.89'). This
413 is useful when conversing with a program that uses the standard C library and
414 needs objects of type :ctype:`struct in_addr`, which is the C type for the
415 32-bit packed binary data this function takes as an argument.
417 If the string passed to this function is not exactly 4 bytes in length,
418 :exc:`socket.error` will be raised. :func:`inet_ntoa` does not support IPv6, and
419 :func:`getnameinfo` should be used instead for IPv4/v6 dual stack support.
422 .. function:: inet_pton(address_family, ip_string)
424 Convert an IP address from its family-specific string format to a packed, binary
425 format. :func:`inet_pton` is useful when a library or network protocol calls for
426 an object of type :ctype:`struct in_addr` (similar to :func:`inet_aton`) or
427 :ctype:`struct in6_addr`.
429 Supported values for *address_family* are currently :const:`AF_INET` and
430 :const:`AF_INET6`. If the IP address string *ip_string* is invalid,
431 :exc:`socket.error` will be raised. Note that exactly what is valid depends on
432 both the value of *address_family* and the underlying implementation of
435 Availability: Unix (maybe not all platforms).
437 .. versionadded:: 2.3
440 .. function:: inet_ntop(address_family, packed_ip)
442 Convert a packed IP address (a string of some number of characters) to its
443 standard, family-specific string representation (for example, ``'7.10.0.5'`` or
444 ``'5aef:2b::8'``) :func:`inet_ntop` is useful when a library or network protocol
445 returns an object of type :ctype:`struct in_addr` (similar to :func:`inet_ntoa`)
446 or :ctype:`struct in6_addr`.
448 Supported values for *address_family* are currently :const:`AF_INET` and
449 :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the
450 specified address family, :exc:`ValueError` will be raised. A
451 :exc:`socket.error` is raised for errors from the call to :func:`inet_ntop`.
453 Availability: Unix (maybe not all platforms).
455 .. versionadded:: 2.3
458 .. function:: getdefaulttimeout()
460 Return the default timeout in floating seconds for new socket objects. A value
461 of ``None`` indicates that new socket objects have no timeout. When the socket
462 module is first imported, the default is ``None``.
464 .. versionadded:: 2.3
467 .. function:: setdefaulttimeout(timeout)
469 Set the default timeout in floating seconds for new socket objects. A value of
470 ``None`` indicates that new socket objects have no timeout. When the socket
471 module is first imported, the default is ``None``.
473 .. versionadded:: 2.3
478 This is a Python type object that represents the socket object type. It is the
479 same as ``type(socket(...))``.
484 Module :mod:`SocketServer`
485 Classes that simplify writing network servers.
493 Socket objects have the following methods. Except for :meth:`makefile` these
494 correspond to Unix system calls applicable to sockets.
497 .. method:: socket.accept()
499 Accept a connection. The socket must be bound to an address and listening for
500 connections. The return value is a pair ``(conn, address)`` where *conn* is a
501 *new* socket object usable to send and receive data on the connection, and
502 *address* is the address bound to the socket on the other end of the connection.
505 .. method:: socket.bind(address)
507 Bind the socket to *address*. The socket must not already be bound. (The format
508 of *address* depends on the address family --- see above.)
512 This method has historically accepted a pair of parameters for :const:`AF_INET`
513 addresses instead of only a tuple. This was never intentional and is no longer
514 available in Python 2.0 and later.
517 .. method:: socket.close()
519 Close the socket. All future operations on the socket object will fail. The
520 remote end will receive no more data (after queued data is flushed). Sockets are
521 automatically closed when they are garbage-collected.
524 .. method:: socket.connect(address)
526 Connect to a remote socket at *address*. (The format of *address* depends on the
527 address family --- see above.)
531 This method has historically accepted a pair of parameters for :const:`AF_INET`
532 addresses instead of only a tuple. This was never intentional and is no longer
533 available in Python 2.0 and later.
536 .. method:: socket.connect_ex(address)
538 Like ``connect(address)``, but return an error indicator instead of raising an
539 exception for errors returned by the C-level :cfunc:`connect` call (other
540 problems, such as "host not found," can still raise exceptions). The error
541 indicator is ``0`` if the operation succeeded, otherwise the value of the
542 :cdata:`errno` variable. This is useful to support, for example, asynchronous
547 This method has historically accepted a pair of parameters for :const:`AF_INET`
548 addresses instead of only a tuple. This was never intentional and is no longer
549 available in Python 2.0 and later.
552 .. method:: socket.fileno()
554 Return the socket's file descriptor (a small integer). This is useful with
555 :func:`select.select`.
557 Under Windows the small integer returned by this method cannot be used where a
558 file descriptor can be used (such as :func:`os.fdopen`). Unix does not have
562 .. method:: socket.getpeername()
564 Return the remote address to which the socket is connected. This is useful to
565 find out the port number of a remote IPv4/v6 socket, for instance. (The format
566 of the address returned depends on the address family --- see above.) On some
567 systems this function is not supported.
570 .. method:: socket.getsockname()
572 Return the socket's own address. This is useful to find out the port number of
573 an IPv4/v6 socket, for instance. (The format of the address returned depends on
574 the address family --- see above.)
577 .. method:: socket.getsockopt(level, optname[, buflen])
579 Return the value of the given socket option (see the Unix man page
580 :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.)
581 are defined in this module. If *buflen* is absent, an integer option is assumed
582 and its integer value is returned by the function. If *buflen* is present, it
583 specifies the maximum length of the buffer used to receive the option in, and
584 this buffer is returned as a string. It is up to the caller to decode the
585 contents of the buffer (see the optional built-in module :mod:`struct` for a way
586 to decode C structures encoded as strings).
589 .. method:: socket.ioctl(control, option)
593 The :meth:`ioctl` method is a limited interface to the WSAIoctl system
594 interface. Please refer to the MSDN documentation for more information.
596 .. versionadded:: 2.6
599 .. method:: socket.listen(backlog)
601 Listen for connections made to the socket. The *backlog* argument specifies the
602 maximum number of queued connections and should be at least 1; the maximum value
603 is system-dependent (usually 5).
606 .. method:: socket.makefile([mode[, bufsize]])
608 .. index:: single: I/O control; buffering
610 Return a :dfn:`file object` associated with the socket. (File objects are
611 described in :ref:`bltin-file-objects`.) The file object
612 references a :cfunc:`dup`\ ped version of the socket file descriptor, so the
613 file object and socket object may be closed or garbage-collected independently.
614 The socket must be in blocking mode (it can not have a timeout). The optional
615 *mode* and *bufsize* arguments are interpreted the same way as by the built-in
616 :func:`file` function.
619 .. method:: socket.recv(bufsize[, flags])
621 Receive data from the socket. The return value is a string representing the
622 data received. The maximum amount of data to be received at once is specified
623 by *bufsize*. See the Unix manual page :manpage:`recv(2)` for the meaning of
624 the optional argument *flags*; it defaults to zero.
628 For best match with hardware and network realities, the value of *bufsize*
629 should be a relatively small power of 2, for example, 4096.
632 .. method:: socket.recvfrom(bufsize[, flags])
634 Receive data from the socket. The return value is a pair ``(string, address)``
635 where *string* is a string representing the data received and *address* is the
636 address of the socket sending the data. See the Unix manual page
637 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
638 to zero. (The format of *address* depends on the address family --- see above.)
641 .. method:: socket.recvfrom_into(buffer[, nbytes[, flags]])
643 Receive data from the socket, writing it into *buffer* instead of creating a
644 new string. The return value is a pair ``(nbytes, address)`` where *nbytes* is
645 the number of bytes received and *address* is the address of the socket sending
646 the data. See the Unix manual page :manpage:`recv(2)` for the meaning of the
647 optional argument *flags*; it defaults to zero. (The format of *address*
648 depends on the address family --- see above.)
650 .. versionadded:: 2.5
653 .. method:: socket.recv_into(buffer[, nbytes[, flags]])
655 Receive up to *nbytes* bytes from the socket, storing the data into a buffer
656 rather than creating a new string. If *nbytes* is not specified (or 0),
657 receive up to the size available in the given buffer. See the Unix manual page
658 :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
661 .. versionadded:: 2.5
664 .. method:: socket.send(string[, flags])
666 Send data to the socket. The socket must be connected to a remote socket. The
667 optional *flags* argument has the same meaning as for :meth:`recv` above.
668 Returns the number of bytes sent. Applications are responsible for checking that
669 all data has been sent; if only some of the data was transmitted, the
670 application needs to attempt delivery of the remaining data.
673 .. method:: socket.sendall(string[, flags])
675 Send data to the socket. The socket must be connected to a remote socket. The
676 optional *flags* argument has the same meaning as for :meth:`recv` above.
677 Unlike :meth:`send`, this method continues to send data from *string* until
678 either all data has been sent or an error occurs. ``None`` is returned on
679 success. On error, an exception is raised, and there is no way to determine how
680 much data, if any, was successfully sent.
683 .. method:: socket.sendto(string[, flags], address)
685 Send data to the socket. The socket should not be connected to a remote socket,
686 since the destination socket is specified by *address*. The optional *flags*
687 argument has the same meaning as for :meth:`recv` above. Return the number of
688 bytes sent. (The format of *address* depends on the address family --- see
692 .. method:: socket.setblocking(flag)
694 Set blocking or non-blocking mode of the socket: if *flag* is 0, the socket is
695 set to non-blocking, else to blocking mode. Initially all sockets are in
696 blocking mode. In non-blocking mode, if a :meth:`recv` call doesn't find any
697 data, or if a :meth:`send` call can't immediately dispose of the data, a
698 :exc:`error` exception is raised; in blocking mode, the calls block until they
699 can proceed. ``s.setblocking(0)`` is equivalent to ``s.settimeout(0)``;
700 ``s.setblocking(1)`` is equivalent to ``s.settimeout(None)``.
703 .. method:: socket.settimeout(value)
705 Set a timeout on blocking socket operations. The *value* argument can be a
706 nonnegative float expressing seconds, or ``None``. If a float is given,
707 subsequent socket operations will raise an :exc:`timeout` exception if the
708 timeout period *value* has elapsed before the operation has completed. Setting
709 a timeout of ``None`` disables timeouts on socket operations.
710 ``s.settimeout(0.0)`` is equivalent to ``s.setblocking(0)``;
711 ``s.settimeout(None)`` is equivalent to ``s.setblocking(1)``.
713 .. versionadded:: 2.3
716 .. method:: socket.gettimeout()
718 Return the timeout in floating seconds associated with socket operations, or
719 ``None`` if no timeout is set. This reflects the last call to
720 :meth:`setblocking` or :meth:`settimeout`.
722 .. versionadded:: 2.3
724 Some notes on socket blocking and timeouts: A socket object can be in one of
725 three modes: blocking, non-blocking, or timeout. Sockets are always created in
726 blocking mode. In blocking mode, operations block until complete. In
727 non-blocking mode, operations fail (with an error that is unfortunately
728 system-dependent) if they cannot be completed immediately. In timeout mode,
729 operations fail if they cannot be completed within the timeout specified for the
730 socket. The :meth:`setblocking` method is simply a shorthand for certain
731 :meth:`settimeout` calls.
733 Timeout mode internally sets the socket in non-blocking mode. The blocking and
734 timeout modes are shared between file descriptors and socket objects that refer
735 to the same network endpoint. A consequence of this is that file objects
736 returned by the :meth:`makefile` method must only be used when the socket is in
737 blocking mode; in timeout or non-blocking mode file operations that cannot be
738 completed immediately will fail.
740 Note that the :meth:`connect` operation is subject to the timeout setting, and
741 in general it is recommended to call :meth:`settimeout` before calling
745 .. method:: socket.setsockopt(level, optname, value)
747 .. index:: module: struct
749 Set the value of the given socket option (see the Unix manual page
750 :manpage:`setsockopt(2)`). The needed symbolic constants are defined in the
751 :mod:`socket` module (:const:`SO_\*` etc.). The value can be an integer or a
752 string representing a buffer. In the latter case it is up to the caller to
753 ensure that the string contains the proper bits (see the optional built-in
754 module :mod:`struct` for a way to encode C structures as strings).
757 .. method:: socket.shutdown(how)
759 Shut down one or both halves of the connection. If *how* is :const:`SHUT_RD`,
760 further receives are disallowed. If *how* is :const:`SHUT_WR`, further sends
761 are disallowed. If *how* is :const:`SHUT_RDWR`, further sends and receives are
764 Note that there are no methods :meth:`read` or :meth:`write`; use :meth:`recv`
765 and :meth:`send` without *flags* argument instead.
767 Socket objects also have these (read-only) attributes that correspond to the
768 values given to the :class:`socket` constructor.
771 .. attribute:: socket.family
775 .. versionadded:: 2.5
778 .. attribute:: socket.type
782 .. versionadded:: 2.5
785 .. attribute:: socket.proto
789 .. versionadded:: 2.5
797 Here are four minimal example programs using the TCP/IP protocol: a server that
798 echoes all data that it receives back (servicing only one client), and a client
799 using it. Note that a server must perform the sequence :func:`socket`,
800 :meth:`bind`, :meth:`listen`, :meth:`accept` (possibly repeating the
801 :meth:`accept` to service more than one client), while a client only needs the
802 sequence :func:`socket`, :meth:`connect`. Also note that the server does not
803 :meth:`send`/:meth:`recv` on the socket it is listening on but on the new
804 socket returned by :meth:`accept`.
806 The first two examples support IPv4 only. ::
808 # Echo server program
811 HOST = '' # Symbolic name meaning the local host
812 PORT = 50007 # Arbitrary non-privileged port
813 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
816 conn, addr = s.accept()
817 print 'Connected by', addr
819 data = conn.recv(1024)
826 # Echo client program
829 HOST = 'daring.cwi.nl' # The remote host
830 PORT = 50007 # The same port as used by the server
831 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
832 s.connect((HOST, PORT))
833 s.send('Hello, world')
836 print 'Received', repr(data)
838 The next two examples are identical to the above two, but support both IPv4 and
839 IPv6. The server side will listen to the first address family available (it
840 should listen to both instead). On most of IPv6-ready systems, IPv6 will take
841 precedence and the server may not accept IPv4 traffic. The client side will try
842 to connect to the all addresses returned as a result of the name resolution, and
843 sends traffic to the first one connected successfully. ::
845 # Echo server program
849 HOST = '' # Symbolic name meaning the local host
850 PORT = 50007 # Arbitrary non-privileged port
852 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM, 0, socket.AI_PASSIVE):
853 af, socktype, proto, canonname, sa = res
855 s = socket.socket(af, socktype, proto)
856 except socket.error, msg:
862 except socket.error, msg:
868 print 'could not open socket'
870 conn, addr = s.accept()
871 print 'Connected by', addr
873 data = conn.recv(1024)
880 # Echo client program
884 HOST = 'daring.cwi.nl' # The remote host
885 PORT = 50007 # The same port as used by the server
887 for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
888 af, socktype, proto, canonname, sa = res
890 s = socket.socket(af, socktype, proto)
891 except socket.error, msg:
896 except socket.error, msg:
902 print 'could not open socket'
904 s.send('Hello, world')
907 print 'Received', repr(data)
910 The last example shows how to write a very simple network sniffer with raw
911 sockets on Windows. The example requires administrator priviliges to modify
916 # the public network interface
917 HOST = socket.gethostbyname(socket.gethostname())
919 # create a raw socket and bind it to the public interface
920 s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP)
924 s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
926 # receive all packages
927 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
930 print s.recvfrom(65565)
932 # disabled promiscous mode
933 s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)