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   1:mod:`socket` --- Low-level networking interface
   2================================================
   3
   4.. module:: socket
   5   :synopsis: Low-level networking interface.
   6
   7
   8This module provides access to the BSD *socket* interface. It is available on
   9all modern Unix systems, Windows, MacOS, OS/2, and probably additional
  10platforms.
  11
  12.. note::
  13
  14   Some behavior may be platform dependent, since calls are made to the operating
  15   system socket APIs.
  16
  17.. index:: object: socket
  18
  19The Python interface is a straightforward transliteration of the Unix system
  20call and library interface for sockets to Python's object-oriented style: the
  21:func:`socket` function returns a :dfn:`socket object` whose methods implement
  22the various socket system calls.  Parameter types are somewhat higher-level than
  23in the C interface: as with :meth:`read` and :meth:`write` operations on Python
  24files, buffer allocation on receive operations is automatic, and buffer length
  25is implicit on send operations.
  26
  27
  28.. seealso::
  29
  30   Module :mod:`socketserver`
  31      Classes that simplify writing network servers.
  32
  33   Module :mod:`ssl`
  34      A TLS/SSL wrapper for socket objects.
  35
  36
  37Socket families
  38---------------
  39
  40Depending on the system and the build options, various socket families
  41are supported by this module.
  42
  43The address format required by a particular socket object is automatically
  44selected based on the address family specified when the socket object was
  45created.  Socket addresses are represented as follows:
  46
  47- The address of an :const:`AF_UNIX` socket bound to a file system node
  48  is represented as a string, using the file system encoding and the
  49  ``'surrogateescape'`` error handler (see :pep:`383`).  An address in
  50  Linux's abstract namespace is returned as a :class:`bytes` object with
  51  an initial null byte; note that sockets in this namespace can
  52  communicate with normal file system sockets, so programs intended to
  53  run on Linux may need to deal with both types of address.  A string or
  54  :class:`bytes` object can be used for either type of address when
  55  passing it as an argument.
  56
  57   .. versionchanged:: 3.3
  58      Previously, :const:`AF_UNIX` socket paths were assumed to use UTF-8
  59      encoding.
  60
  61- A pair ``(host, port)`` is used for the :const:`AF_INET` address family,
  62  where *host* is a string representing either a hostname in Internet domain
  63  notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``,
  64  and *port* is an integer.
  65
  66- For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo,
  67  scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo``
  68  and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C.  For
  69  :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for
  70  backward compatibility.  Note, however, omission of *scopeid* can cause problems
  71  in manipulating scoped IPv6 addresses.
  72
  73- :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``.
  74
  75- Linux-only support for TIPC is available using the :const:`AF_TIPC`
  76  address family.  TIPC is an open, non-IP based networked protocol designed
  77  for use in clustered computer environments.  Addresses are represented by a
  78  tuple, and the fields depend on the address type. The general tuple form is
  79  ``(addr_type, v1, v2, v3 [, scope])``, where:
  80
  81  - *addr_type* is one of :const:`TIPC_ADDR_NAMESEQ`, :const:`TIPC_ADDR_NAME`,
  82    or :const:`TIPC_ADDR_ID`.
  83  - *scope* is one of :const:`TIPC_ZONE_SCOPE`, :const:`TIPC_CLUSTER_SCOPE`, and
  84    :const:`TIPC_NODE_SCOPE`.
  85  - If *addr_type* is :const:`TIPC_ADDR_NAME`, then *v1* is the server type, *v2* is
  86    the port identifier, and *v3* should be 0.
  87
  88    If *addr_type* is :const:`TIPC_ADDR_NAMESEQ`, then *v1* is the server type, *v2*
  89    is the lower port number, and *v3* is the upper port number.
  90
  91    If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the
  92    reference, and *v3* should be set to 0.
  93
  94    If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the
  95    reference, and *v3* should be set to 0.
  96
  97- A tuple ``(interface, )`` is used for the :const:`AF_CAN` address family,
  98  where *interface* is a string representing a network interface name like
  99  ``'can0'``. The network interface name ``''`` can be used to receive packets
 100  from all network interfaces of this family.
 101
 102- A string or a tuple ``(id, unit)`` is used for the :const:`SYSPROTO_CONTROL`
 103  protocol of the :const:`PF_SYSTEM` family. The string is the name of a
 104  kernel control using a dynamically-assigned ID. The tuple can be used if ID
 105  and unit number of the kernel control are known or if a registered ID is
 106  used.
 107
 108  .. versionadded:: 3.3
 109
 110- Certain other address families (:const:`AF_BLUETOOTH`, :const:`AF_PACKET`)
 111  support specific representations.
 112
 113  .. XXX document them!
 114
 115For IPv4 addresses, two special forms are accepted instead of a host address:
 116the empty string represents :const:`INADDR_ANY`, and the string
 117``'<broadcast>'`` represents :const:`INADDR_BROADCAST`.  This behavior is not
 118compatible with IPv6, therefore, you may want to avoid these if you intend
 119to support IPv6 with your Python programs.
 120
 121If you use a hostname in the *host* portion of IPv4/v6 socket address, the
 122program may show a nondeterministic behavior, as Python uses the first address
 123returned from the DNS resolution.  The socket address will be resolved
 124differently into an actual IPv4/v6 address, depending on the results from DNS
 125resolution and/or the host configuration.  For deterministic behavior use a
 126numeric address in *host* portion.
 127
 128All errors raise exceptions.  The normal exceptions for invalid argument types
 129and out-of-memory conditions can be raised; starting from Python 3.3, errors
 130related to socket or address semantics raise :exc:`OSError` or one of its
 131subclasses (they used to raise :exc:`socket.error`).
 132
 133Non-blocking mode is supported through :meth:`~socket.setblocking`.  A
 134generalization of this based on timeouts is supported through
 135:meth:`~socket.settimeout`.
 136
 137
 138Module contents
 139---------------
 140
 141The module :mod:`socket` exports the following constants and functions:
 142
 143
 144.. exception:: error
 145
 146   A deprecated alias of :exc:`OSError`.
 147
 148   .. versionchanged:: 3.3
 149      Following :pep:`3151`, this class was made an alias of :exc:`OSError`.
 150
 151
 152.. exception:: herror
 153
 154   A subclass of :exc:`OSError`, this exception is raised for
 155   address-related errors, i.e. for functions that use *h_errno* in the POSIX
 156   C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`.
 157   The accompanying value is a pair ``(h_errno, string)`` representing an
 158   error returned by a library call.  *h_errno* is a numeric value, while
 159   *string* represents the description of *h_errno*, as returned by the
 160   :c:func:`hstrerror` C function.
 161
 162   .. versionchanged:: 3.3
 163      This class was made a subclass of :exc:`OSError`.
 164
 165.. exception:: gaierror
 166
 167   A subclass of :exc:`OSError`, this exception is raised for
 168   address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`.
 169   The accompanying value is a pair ``(error, string)`` representing an error
 170   returned by a library call.  *string* represents the description of
 171   *error*, as returned by the :c:func:`gai_strerror` C function.  The
 172   numeric *error* value will match one of the :const:`EAI_\*` constants
 173   defined in this module.
 174
 175   .. versionchanged:: 3.3
 176      This class was made a subclass of :exc:`OSError`.
 177
 178.. exception:: timeout
 179
 180   A subclass of :exc:`OSError`, this exception is raised when a timeout
 181   occurs on a socket which has had timeouts enabled via a prior call to
 182   :meth:`~socket.settimeout` (or implicitly through
 183   :func:`~socket.setdefaulttimeout`).  The accompanying value is a string
 184   whose value is currently always "timed out".
 185
 186   .. versionchanged:: 3.3
 187      This class was made a subclass of :exc:`OSError`.
 188
 189.. data:: AF_UNIX
 190          AF_INET
 191          AF_INET6
 192
 193   These constants represent the address (and protocol) families, used for the
 194   first argument to :func:`socket`.  If the :const:`AF_UNIX` constant is not
 195   defined then this protocol is unsupported.  More constants may be available
 196   depending on the system.
 197
 198
 199.. data:: SOCK_STREAM
 200          SOCK_DGRAM
 201          SOCK_RAW
 202          SOCK_RDM
 203          SOCK_SEQPACKET
 204
 205   These constants represent the socket types, used for the second argument to
 206   :func:`socket`.  More constants may be available depending on the system.
 207   (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally
 208   useful.)
 209
 210.. data:: SOCK_CLOEXEC
 211          SOCK_NONBLOCK
 212
 213   These two constants, if defined, can be combined with the socket types and
 214   allow you to set some flags atomically (thus avoiding possible race
 215   conditions and the need for separate calls).
 216
 217   .. seealso::
 218
 219      `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_
 220      for a more thorough explanation.
 221
 222   Availability: Linux >= 2.6.27.
 223
 224   .. versionadded:: 3.2
 225
 226.. data:: SO_*
 227          SOMAXCONN
 228          MSG_*
 229          SOL_*
 230          SCM_*
 231          IPPROTO_*
 232          IPPORT_*
 233          INADDR_*
 234          IP_*
 235          IPV6_*
 236          EAI_*
 237          AI_*
 238          NI_*
 239          TCP_*
 240
 241   Many constants of these forms, documented in the Unix documentation on sockets
 242   and/or the IP protocol, are also defined in the socket module. They are
 243   generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt`
 244   methods of socket objects.  In most cases, only those symbols that are defined
 245   in the Unix header files are defined; for a few symbols, default values are
 246   provided.
 247
 248.. data:: AF_CAN
 249          PF_CAN
 250          SOL_CAN_*
 251          CAN_*
 252
 253   Many constants of these forms, documented in the Linux documentation, are
 254   also defined in the socket module.
 255
 256   Availability: Linux >= 2.6.25.
 257
 258   .. versionadded:: 3.3
 259
 260
 261.. data:: AF_RDS
 262          PF_RDS
 263          SOL_RDS
 264          RDS_*
 265
 266   Many constants of these forms, documented in the Linux documentation, are
 267   also defined in the socket module.
 268
 269   Availability: Linux >= 2.6.30.
 270
 271   .. versionadded:: 3.3
 272
 273
 274.. data:: SIO_*
 275          RCVALL_*
 276
 277   Constants for Windows' WSAIoctl(). The constants are used as arguments to the
 278   :meth:`ioctl` method of socket objects.
 279
 280
 281.. data:: TIPC_*
 282
 283   TIPC related constants, matching the ones exported by the C socket API. See
 284   the TIPC documentation for more information.
 285
 286
 287.. data:: has_ipv6
 288
 289   This constant contains a boolean value which indicates if IPv6 is supported on
 290   this platform.
 291
 292
 293.. function:: create_connection(address[, timeout[, source_address]])
 294
 295   Connect to a TCP service listening on the Internet *address* (a 2-tuple
 296   ``(host, port)``), and return the socket object.  This is a higher-level
 297   function than :meth:`socket.connect`: if *host* is a non-numeric hostname,
 298   it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`,
 299   and then try to connect to all possible addresses in turn until a
 300   connection succeeds.  This makes it easy to write clients that are
 301   compatible to both IPv4 and IPv6.
 302
 303   Passing the optional *timeout* parameter will set the timeout on the
 304   socket instance before attempting to connect.  If no *timeout* is
 305   supplied, the global default timeout setting returned by
 306   :func:`getdefaulttimeout` is used.
 307
 308   If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the
 309   socket to bind to as its source address before connecting.  If host or port
 310   are '' or 0 respectively the OS default behavior will be used.
 311
 312   .. versionchanged:: 3.2
 313      *source_address* was added.
 314
 315   .. versionchanged:: 3.2
 316      support for the :keyword:`with` statement was added.
 317
 318
 319.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0)
 320
 321   Translate the *host*/*port* argument into a sequence of 5-tuples that contain
 322   all the necessary arguments for creating a socket connected to that service.
 323   *host* is a domain name, a string representation of an IPv4/v6 address
 324   or ``None``. *port* is a string service name such as ``'http'``, a numeric
 325   port number or ``None``.  By passing ``None`` as the value of *host*
 326   and *port*, you can pass ``NULL`` to the underlying C API.
 327
 328   The *family*, *type* and *proto* arguments can be optionally specified
 329   in order to narrow the list of addresses returned.  Passing zero as a
 330   value for each of these arguments selects the full range of results.
 331   The *flags* argument can be one or several of the ``AI_*`` constants,
 332   and will influence how results are computed and returned.
 333   For example, :const:`AI_NUMERICHOST` will disable domain name resolution
 334   and will raise an error if *host* is a domain name.
 335
 336   The function returns a list of 5-tuples with the following structure:
 337
 338   ``(family, type, proto, canonname, sockaddr)``
 339
 340   In these tuples, *family*, *type*, *proto* are all integers and are
 341   meant to be passed to the :func:`socket` function.  *canonname* will be
 342   a string representing the canonical name of the *host* if
 343   :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname*
 344   will be empty.  *sockaddr* is a tuple describing a socket address, whose
 345   format depends on the returned *family* (a ``(address, port)`` 2-tuple for
 346   :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for
 347   :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect`
 348   method.
 349
 350   The following example fetches address information for a hypothetical TCP
 351   connection to ``www.python.org`` on port 80 (results may differ on your
 352   system if IPv6 isn't enabled)::
 353
 354      >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP)
 355      [(2, 1, 6, '', ('82.94.164.162', 80)),
 356       (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))]
 357
 358   .. versionchanged:: 3.2
 359      parameters can now be passed as single keyword arguments.
 360
 361.. function:: getfqdn([name])
 362
 363   Return a fully qualified domain name for *name*. If *name* is omitted or empty,
 364   it is interpreted as the local host.  To find the fully qualified name, the
 365   hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the
 366   host, if available.  The first name which includes a period is selected.  In
 367   case no fully qualified domain name is available, the hostname as returned by
 368   :func:`gethostname` is returned.
 369
 370
 371.. function:: gethostbyname(hostname)
 372
 373   Translate a host name to IPv4 address format.  The IPv4 address is returned as a
 374   string, such as  ``'100.50.200.5'``.  If the host name is an IPv4 address itself
 375   it is returned unchanged.  See :func:`gethostbyname_ex` for a more complete
 376   interface. :func:`gethostbyname` does not support IPv6 name resolution, and
 377   :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support.
 378
 379
 380.. function:: gethostbyname_ex(hostname)
 381
 382   Translate a host name to IPv4 address format, extended interface. Return a
 383   triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary
 384   host name responding to the given *ip_address*, *aliaslist* is a (possibly
 385   empty) list of alternative host names for the same address, and *ipaddrlist* is
 386   a list of IPv4 addresses for the same interface on the same host (often but not
 387   always a single address). :func:`gethostbyname_ex` does not support IPv6 name
 388   resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual
 389   stack support.
 390
 391
 392.. function:: gethostname()
 393
 394   Return a string containing the hostname of the machine where  the Python
 395   interpreter is currently executing.
 396
 397   If you want to know the current machine's IP address, you may want to use
 398   ``gethostbyname(gethostname())``. This operation assumes that there is a
 399   valid address-to-host mapping for the host, and the assumption does not
 400   always hold.
 401
 402   Note: :func:`gethostname` doesn't always return the fully qualified domain
 403   name; use ``getfqdn()`` (see above).
 404
 405
 406.. function:: gethostbyaddr(ip_address)
 407
 408   Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the
 409   primary host name responding to the given *ip_address*, *aliaslist* is a
 410   (possibly empty) list of alternative host names for the same address, and
 411   *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same
 412   host (most likely containing only a single address). To find the fully qualified
 413   domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports
 414   both IPv4 and IPv6.
 415
 416
 417.. function:: getnameinfo(sockaddr, flags)
 418
 419   Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending
 420   on the settings of *flags*, the result can contain a fully-qualified domain name
 421   or numeric address representation in *host*.  Similarly, *port* can contain a
 422   string port name or a numeric port number.
 423
 424
 425.. function:: getprotobyname(protocolname)
 426
 427   Translate an Internet protocol name (for example, ``'icmp'``) to a constant
 428   suitable for passing as the (optional) third argument to the :func:`socket`
 429   function.  This is usually only needed for sockets opened in "raw" mode
 430   (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen
 431   automatically if the protocol is omitted or zero.
 432
 433
 434.. function:: getservbyname(servicename[, protocolname])
 435
 436   Translate an Internet service name and protocol name to a port number for that
 437   service.  The optional protocol name, if given, should be ``'tcp'`` or
 438   ``'udp'``, otherwise any protocol will match.
 439
 440
 441.. function:: getservbyport(port[, protocolname])
 442
 443   Translate an Internet port number and protocol name to a service name for that
 444   service.  The optional protocol name, if given, should be ``'tcp'`` or
 445   ``'udp'``, otherwise any protocol will match.
 446
 447
 448.. function:: socket([family[, type[, proto]]], cloexec=True)
 449
 450   Create a new socket using the given address family, socket type and protocol
 451   number.  The address family should be :const:`AF_INET` (the default),
 452   :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The
 453   socket type should be :const:`SOCK_STREAM` (the default),
 454   :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_``
 455   constants. The protocol number is usually zero and may be omitted in that
 456   case or :const:`CAN_RAW` in case the address family is :const:`AF_CAN`.
 457
 458   If *cloexec* is ``True``, set :ref:`close-on-exec flag <cloexec>`.
 459
 460   .. versionchanged:: 3.3
 461      The AF_CAN family was added.
 462      The AF_RDS family was added.
 463
 464   .. versionchanged:: 3.4
 465      *cloexec* parameter was added.
 466
 467
 468.. function:: socketpair([family[, type[, proto]]], cloexec=True)
 469
 470   Build a pair of connected socket objects using the given address family, socket
 471   type, and protocol number.  Address family, socket type, and protocol number are
 472   as for the :func:`socket` function above. The default family is :const:`AF_UNIX`
 473   if defined on the platform; otherwise, the default is :const:`AF_INET`.
 474
 475   If *cloexec* is ``True``, set :ref:`close-on-exec flag <cloexec>`.
 476
 477   Availability: Unix.
 478
 479   .. versionchanged:: 3.2
 480      The returned socket objects now support the whole socket API, rather
 481      than a subset.
 482
 483   .. versionchanged:: 3.4
 484      *cloexec* parameter was added.
 485
 486
 487.. function:: fromfd(fd, family, type[, proto])
 488
 489   Duplicate the file descriptor *fd* (an integer as returned by a file object's
 490   :meth:`fileno` method) and build a socket object from the result.  Address
 491   family, socket type and protocol number are as for the :func:`socket` function
 492   above. The file descriptor should refer to a socket, but this is not checked ---
 493   subsequent operations on the object may fail if the file descriptor is invalid.
 494   This function is rarely needed, but can be used to get or set socket options on
 495   a socket passed to a program as standard input or output (such as a server
 496   started by the Unix inet daemon).  The socket is assumed to be in blocking mode.
 497
 498
 499.. function:: ntohl(x)
 500
 501   Convert 32-bit positive integers from network to host byte order.  On machines
 502   where the host byte order is the same as network byte order, this is a no-op;
 503   otherwise, it performs a 4-byte swap operation.
 504
 505
 506.. function:: ntohs(x)
 507
 508   Convert 16-bit positive integers from network to host byte order.  On machines
 509   where the host byte order is the same as network byte order, this is a no-op;
 510   otherwise, it performs a 2-byte swap operation.
 511
 512
 513.. function:: htonl(x)
 514
 515   Convert 32-bit positive integers from host to network byte order.  On machines
 516   where the host byte order is the same as network byte order, this is a no-op;
 517   otherwise, it performs a 4-byte swap operation.
 518
 519
 520.. function:: htons(x)
 521
 522   Convert 16-bit positive integers from host to network byte order.  On machines
 523   where the host byte order is the same as network byte order, this is a no-op;
 524   otherwise, it performs a 2-byte swap operation.
 525
 526
 527.. function:: inet_aton(ip_string)
 528
 529   Convert an IPv4 address from dotted-quad string format (for example,
 530   '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in
 531   length.  This is useful when conversing with a program that uses the standard C
 532   library and needs objects of type :c:type:`struct in_addr`, which is the C type
 533   for the 32-bit packed binary this function returns.
 534
 535   :func:`inet_aton` also accepts strings with less than three dots; see the
 536   Unix manual page :manpage:`inet(3)` for details.
 537
 538   If the IPv4 address string passed to this function is invalid,
 539   :exc:`OSError` will be raised. Note that exactly what is valid depends on
 540   the underlying C implementation of :c:func:`inet_aton`.
 541
 542   :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used
 543   instead for IPv4/v6 dual stack support.
 544
 545
 546.. function:: inet_ntoa(packed_ip)
 547
 548   Convert a 32-bit packed IPv4 address (a bytes object four characters in
 549   length) to its standard dotted-quad string representation (for example,
 550   '123.45.67.89').  This is useful when conversing with a program that uses the
 551   standard C library and needs objects of type :c:type:`struct in_addr`, which
 552   is the C type for the 32-bit packed binary data this function takes as an
 553   argument.
 554
 555   If the byte sequence passed to this function is not exactly 4 bytes in
 556   length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not
 557   support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual
 558   stack support.
 559
 560
 561.. function:: inet_pton(address_family, ip_string)
 562
 563   Convert an IP address from its family-specific string format to a packed,
 564   binary format. :func:`inet_pton` is useful when a library or network protocol
 565   calls for an object of type :c:type:`struct in_addr` (similar to
 566   :func:`inet_aton`) or :c:type:`struct in6_addr`.
 567
 568   Supported values for *address_family* are currently :const:`AF_INET` and
 569   :const:`AF_INET6`. If the IP address string *ip_string* is invalid,
 570   :exc:`OSError` will be raised. Note that exactly what is valid depends on
 571   both the value of *address_family* and the underlying implementation of
 572   :c:func:`inet_pton`.
 573
 574   Availability: Unix (maybe not all platforms).
 575
 576
 577.. function:: inet_ntop(address_family, packed_ip)
 578
 579   Convert a packed IP address (a bytes object of some number of characters) to its
 580   standard, family-specific string representation (for example, ``'7.10.0.5'`` or
 581   ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol
 582   returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`)
 583   or :c:type:`struct in6_addr`.
 584
 585   Supported values for *address_family* are currently :const:`AF_INET` and
 586   :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the
 587   specified address family, :exc:`ValueError` will be raised.  A
 588   :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`.
 589
 590   Availability: Unix (maybe not all platforms).
 591
 592
 593..
 594   XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any
 595   non-Unix platforms?  The old (obsolete?) 4.2BSD form of the
 596   interface, in which struct msghdr has no msg_control or
 597   msg_controllen members, is not currently supported.
 598
 599.. function:: CMSG_LEN(length)
 600
 601   Return the total length, without trailing padding, of an ancillary
 602   data item with associated data of the given *length*.  This value
 603   can often be used as the buffer size for :meth:`~socket.recvmsg` to
 604   receive a single item of ancillary data, but :rfc:`3542` requires
 605   portable applications to use :func:`CMSG_SPACE` and thus include
 606   space for padding, even when the item will be the last in the
 607   buffer.  Raises :exc:`OverflowError` if *length* is outside the
 608   permissible range of values.
 609
 610   Availability: most Unix platforms, possibly others.
 611
 612   .. versionadded:: 3.3
 613
 614
 615.. function:: CMSG_SPACE(length)
 616
 617   Return the buffer size needed for :meth:`~socket.recvmsg` to
 618   receive an ancillary data item with associated data of the given
 619   *length*, along with any trailing padding.  The buffer space needed
 620   to receive multiple items is the sum of the :func:`CMSG_SPACE`
 621   values for their associated data lengths.  Raises
 622   :exc:`OverflowError` if *length* is outside the permissible range
 623   of values.
 624
 625   Note that some systems might support ancillary data without
 626   providing this function.  Also note that setting the buffer size
 627   using the results of this function may not precisely limit the
 628   amount of ancillary data that can be received, since additional
 629   data may be able to fit into the padding area.
 630
 631   Availability: most Unix platforms, possibly others.
 632
 633   .. versionadded:: 3.3
 634
 635
 636.. function:: getdefaulttimeout()
 637
 638   Return the default timeout in seconds (float) for new socket objects. A value
 639   of ``None`` indicates that new socket objects have no timeout. When the socket
 640   module is first imported, the default is ``None``.
 641
 642
 643.. function:: setdefaulttimeout(timeout)
 644
 645   Set the default timeout in seconds (float) for new socket objects.  When
 646   the socket module is first imported, the default is ``None``.  See
 647   :meth:`~socket.settimeout` for possible values and their respective
 648   meanings.
 649
 650
 651.. function:: sethostname(name)
 652
 653   Set the machine's hostname to *name*.  This will raise a
 654   :exc:`OSError` if you don't have enough rights.
 655
 656   Availability: Unix.
 657
 658   .. versionadded:: 3.3
 659
 660
 661.. function:: if_nameindex()
 662
 663   Return a list of network interface information
 664   (index int, name string) tuples.
 665   :exc:`OSError` if the system call fails.
 666
 667   Availability: Unix.
 668
 669   .. versionadded:: 3.3
 670
 671
 672.. function:: if_nametoindex(if_name)
 673
 674   Return a network interface index number corresponding to an
 675   interface name.
 676   :exc:`OSError` if no interface with the given name exists.
 677
 678   Availability: Unix.
 679
 680   .. versionadded:: 3.3
 681
 682
 683.. function:: if_indextoname(if_index)
 684
 685   Return a network interface name corresponding to a
 686   interface index number.
 687   :exc:`OSError` if no interface with the given index exists.
 688
 689   Availability: Unix.
 690
 691   .. versionadded:: 3.3
 692
 693
 694.. function:: fromshare(data)
 695
 696   Instantiate a socket from data obtained from :meth:`~socket.share`.
 697   The socket is assumed to be in blocking mode.
 698
 699   Availability: Windows.
 700
 701   .. versionadded:: 3.3
 702
 703
 704.. data:: SocketType
 705
 706   This is a Python type object that represents the socket object type. It is the
 707   same as ``type(socket(...))``.
 708
 709
 710.. _socket-objects:
 711
 712Socket Objects
 713--------------
 714
 715Socket objects have the following methods.  Except for :meth:`makefile` these
 716correspond to Unix system calls applicable to sockets.
 717
 718
 719.. method:: socket.accept(cloexec=True)
 720
 721   Accept a connection. The socket must be bound to an address and listening for
 722   connections. The return value is a pair ``(conn, address)`` where *conn* is a
 723   *new* socket object usable to send and receive data on the connection, and
 724   *address* is the address bound to the socket on the other end of the connection.
 725
 726   If *cloexec* is ``True``, set :ref:`close-on-exec flag <cloexec>`.
 727
 728   .. versionchanged:: 3.4
 729      *cloexec* parameter was added.
 730
 731
 732.. method:: socket.bind(address)
 733
 734   Bind the socket to *address*.  The socket must not already be bound. (The format
 735   of *address* depends on the address family --- see above.)
 736
 737
 738.. method:: socket.close()
 739
 740   Close the socket.  All future operations on the socket object will fail. The
 741   remote end will receive no more data (after queued data is flushed). Sockets are
 742   automatically closed when they are garbage-collected.
 743
 744   .. note::
 745      :meth:`close()` releases the resource associated with a connection but
 746      does not necessarily close the connection immediately.  If you want
 747      to close the connection in a timely fashion, call :meth:`shutdown()`
 748      before :meth:`close()`.
 749
 750
 751.. method:: socket.connect(address)
 752
 753   Connect to a remote socket at *address*. (The format of *address* depends on the
 754   address family --- see above.)
 755
 756
 757.. method:: socket.connect_ex(address)
 758
 759   Like ``connect(address)``, but return an error indicator instead of raising an
 760   exception for errors returned by the C-level :c:func:`connect` call (other
 761   problems, such as "host not found," can still raise exceptions).  The error
 762   indicator is ``0`` if the operation succeeded, otherwise the value of the
 763   :c:data:`errno` variable.  This is useful to support, for example, asynchronous
 764   connects.
 765
 766
 767.. method:: socket.detach()
 768
 769   Put the socket object into closed state without actually closing the
 770   underlying file descriptor.  The file descriptor is returned, and can
 771   be reused for other purposes.
 772
 773   .. versionadded:: 3.2
 774
 775
 776.. method:: socket.fileno()
 777
 778   Return the socket's file descriptor (a small integer).  This is useful with
 779   :func:`select.select`.
 780
 781   Under Windows the small integer returned by this method cannot be used where a
 782   file descriptor can be used (such as :func:`os.fdopen`).  Unix does not have
 783   this limitation.
 784
 785
 786.. method:: socket.getpeername()
 787
 788   Return the remote address to which the socket is connected.  This is useful to
 789   find out the port number of a remote IPv4/v6 socket, for instance. (The format
 790   of the address returned depends on the address family --- see above.)  On some
 791   systems this function is not supported.
 792
 793
 794.. method:: socket.getsockname()
 795
 796   Return the socket's own address.  This is useful to find out the port number of
 797   an IPv4/v6 socket, for instance. (The format of the address returned depends on
 798   the address family --- see above.)
 799
 800
 801.. method:: socket.getsockopt(level, optname[, buflen])
 802
 803   Return the value of the given socket option (see the Unix man page
 804   :manpage:`getsockopt(2)`).  The needed symbolic constants (:const:`SO_\*` etc.)
 805   are defined in this module.  If *buflen* is absent, an integer option is assumed
 806   and its integer value is returned by the function.  If *buflen* is present, it
 807   specifies the maximum length of the buffer used to receive the option in, and
 808   this buffer is returned as a bytes object.  It is up to the caller to decode the
 809   contents of the buffer (see the optional built-in module :mod:`struct` for a way
 810   to decode C structures encoded as byte strings).
 811
 812
 813.. method:: socket.gettimeout()
 814
 815   Return the timeout in seconds (float) associated with socket operations,
 816   or ``None`` if no timeout is set.  This reflects the last call to
 817   :meth:`setblocking` or :meth:`settimeout`.
 818
 819
 820.. method:: socket.ioctl(control, option)
 821
 822   :platform: Windows
 823
 824   The :meth:`ioctl` method is a limited interface to the WSAIoctl system
 825   interface.  Please refer to the `Win32 documentation
 826   <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more
 827   information.
 828
 829   On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl`
 830   functions may be used; they accept a socket object as their first argument.
 831
 832.. method:: socket.listen(backlog)
 833
 834   Listen for connections made to the socket.  The *backlog* argument specifies the
 835   maximum number of queued connections and should be at least 0; the maximum value
 836   is system-dependent (usually 5), the minimum value is forced to 0.
 837
 838
 839.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \
 840                            errors=None, newline=None)
 841
 842   .. index:: single: I/O control; buffering
 843
 844   Return a :term:`file object` associated with the socket.  The exact returned
 845   type depends on the arguments given to :meth:`makefile`.  These arguments are
 846   interpreted the same way as by the built-in :func:`open` function.
 847
 848   Closing the file object won't close the socket unless there are no remaining
 849   references to the socket.  The socket must be in blocking mode; it can have
 850   a timeout, but the file object's internal buffer may end up in a inconsistent
 851   state if a timeout occurs.
 852
 853   .. note::
 854
 855      On Windows, the file-like object created by :meth:`makefile` cannot be
 856      used where a file object with a file descriptor is expected, such as the
 857      stream arguments of :meth:`subprocess.Popen`.
 858
 859
 860.. method:: socket.recv(bufsize[, flags])
 861
 862   Receive data from the socket.  The return value is a bytes object representing the
 863   data received.  The maximum amount of data to be received at once is specified
 864   by *bufsize*.  See the Unix manual page :manpage:`recv(2)` for the meaning of
 865   the optional argument *flags*; it defaults to zero.
 866
 867   .. note::
 868
 869      For best match with hardware and network realities, the value of  *bufsize*
 870      should be a relatively small power of 2, for example, 4096.
 871
 872
 873.. method:: socket.recvfrom(bufsize[, flags])
 874
 875   Receive data from the socket.  The return value is a pair ``(bytes, address)``
 876   where *bytes* is a bytes object representing the data received and *address* is the
 877   address of the socket sending the data.  See the Unix manual page
 878   :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
 879   to zero. (The format of *address* depends on the address family --- see above.)
 880
 881
 882.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]])
 883
 884   Receive normal data (up to *bufsize* bytes) and ancillary data from
 885   the socket.  The *ancbufsize* argument sets the size in bytes of
 886   the internal buffer used to receive the ancillary data; it defaults
 887   to 0, meaning that no ancillary data will be received.  Appropriate
 888   buffer sizes for ancillary data can be calculated using
 889   :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit
 890   into the buffer might be truncated or discarded.  The *flags*
 891   argument defaults to 0 and has the same meaning as for
 892   :meth:`recv`.
 893
 894   The return value is a 4-tuple: ``(data, ancdata, msg_flags,
 895   address)``.  The *data* item is a :class:`bytes` object holding the
 896   non-ancillary data received.  The *ancdata* item is a list of zero
 897   or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing
 898   the ancillary data (control messages) received: *cmsg_level* and
 899   *cmsg_type* are integers specifying the protocol level and
 900   protocol-specific type respectively, and *cmsg_data* is a
 901   :class:`bytes` object holding the associated data.  The *msg_flags*
 902   item is the bitwise OR of various flags indicating conditions on
 903   the received message; see your system documentation for details.
 904   If the receiving socket is unconnected, *address* is the address of
 905   the sending socket, if available; otherwise, its value is
 906   unspecified.
 907
 908   On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to
 909   pass file descriptors between processes over an :const:`AF_UNIX`
 910   socket.  When this facility is used (it is often restricted to
 911   :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its
 912   ancillary data, items of the form ``(socket.SOL_SOCKET,
 913   socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object
 914   representing the new file descriptors as a binary array of the
 915   native C :c:type:`int` type.  If :meth:`recvmsg` raises an
 916   exception after the system call returns, it will first attempt to
 917   close any file descriptors received via this mechanism.
 918
 919   Some systems do not indicate the truncated length of ancillary data
 920   items which have been only partially received.  If an item appears
 921   to extend beyond the end of the buffer, :meth:`recvmsg` will issue
 922   a :exc:`RuntimeWarning`, and will return the part of it which is
 923   inside the buffer provided it has not been truncated before the
 924   start of its associated data.
 925
 926   On systems which support the :const:`SCM_RIGHTS` mechanism, the
 927   following function will receive up to *maxfds* file descriptors,
 928   returning the message data and a list containing the descriptors
 929   (while ignoring unexpected conditions such as unrelated control
 930   messages being received).  See also :meth:`sendmsg`. ::
 931
 932      import socket, array
 933
 934      def recv_fds(sock, msglen, maxfds):
 935          fds = array.array("i")   # Array of ints
 936          msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
 937          for cmsg_level, cmsg_type, cmsg_data in ancdata:
 938              if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
 939                  # Append data, ignoring any truncated integers at the end.
 940                  fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
 941          return msg, list(fds)
 942
 943   Availability: most Unix platforms, possibly others.
 944
 945   .. versionadded:: 3.3
 946
 947
 948.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]])
 949
 950   Receive normal data and ancillary data from the socket, behaving as
 951   :meth:`recvmsg` would, but scatter the non-ancillary data into a
 952   series of buffers instead of returning a new bytes object.  The
 953   *buffers* argument must be an iterable of objects that export
 954   writable buffers (e.g. :class:`bytearray` objects); these will be
 955   filled with successive chunks of the non-ancillary data until it
 956   has all been written or there are no more buffers.  The operating
 957   system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``)
 958   on the number of buffers that can be used.  The *ancbufsize* and
 959   *flags* arguments have the same meaning as for :meth:`recvmsg`.
 960
 961   The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags,
 962   address)``, where *nbytes* is the total number of bytes of
 963   non-ancillary data written into the buffers, and *ancdata*,
 964   *msg_flags* and *address* are the same as for :meth:`recvmsg`.
 965
 966   Example::
 967
 968      >>> import socket
 969      >>> s1, s2 = socket.socketpair()
 970      >>> b1 = bytearray(b'----')
 971      >>> b2 = bytearray(b'0123456789')
 972      >>> b3 = bytearray(b'--------------')
 973      >>> s1.send(b'Mary had a little lamb')
 974      22
 975      >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3])
 976      (22, [], 0, None)
 977      >>> [b1, b2, b3]
 978      [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')]
 979
 980   Availability: most Unix platforms, possibly others.
 981
 982   .. versionadded:: 3.3
 983
 984
 985.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]])
 986
 987   Receive data from the socket, writing it into *buffer* instead of creating a
 988   new bytestring.  The return value is a pair ``(nbytes, address)`` where *nbytes* is
 989   the number of bytes received and *address* is the address of the socket sending
 990   the data.  See the Unix manual page :manpage:`recv(2)` for the meaning of the
 991   optional argument *flags*; it defaults to zero.  (The format of *address*
 992   depends on the address family --- see above.)
 993
 994
 995.. method:: socket.recv_into(buffer[, nbytes[, flags]])
 996
 997   Receive up to *nbytes* bytes from the socket, storing the data into a buffer
 998   rather than creating a new bytestring.  If *nbytes* is not specified (or 0),
 999   receive up to the size available in the given buffer.  Returns the number of
1000   bytes received.  See the Unix manual page :manpage:`recv(2)` for the meaning
1001   of the optional argument *flags*; it defaults to zero.
1002
1003
1004.. method:: socket.send(bytes[, flags])
1005
1006   Send data to the socket.  The socket must be connected to a remote socket.  The
1007   optional *flags* argument has the same meaning as for :meth:`recv` above.
1008   Returns the number of bytes sent. Applications are responsible for checking that
1009   all data has been sent; if only some of the data was transmitted, the
1010   application needs to attempt delivery of the remaining data. For further
1011   information on this topic, consult the :ref:`socket-howto`.
1012
1013
1014.. method:: socket.sendall(bytes[, flags])
1015
1016   Send data to the socket.  The socket must be connected to a remote socket.  The
1017   optional *flags* argument has the same meaning as for :meth:`recv` above.
1018   Unlike :meth:`send`, this method continues to send data from *bytes* until
1019   either all data has been sent or an error occurs.  ``None`` is returned on
1020   success.  On error, an exception is raised, and there is no way to determine how
1021   much data, if any, was successfully sent.
1022
1023
1024.. method:: socket.sendto(bytes, address)
1025            socket.sendto(bytes, flags, address)
1026
1027   Send data to the socket.  The socket should not be connected to a remote socket,
1028   since the destination socket is specified by *address*.  The optional *flags*
1029   argument has the same meaning as for :meth:`recv` above.  Return the number of
1030   bytes sent. (The format of *address* depends on the address family --- see
1031   above.)
1032
1033
1034.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]])
1035
1036   Send normal and ancillary data to the socket, gathering the
1037   non-ancillary data from a series of buffers and concatenating it
1038   into a single message.  The *buffers* argument specifies the
1039   non-ancillary data as an iterable of buffer-compatible objects
1040   (e.g. :class:`bytes` objects); the operating system may set a limit
1041   (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers
1042   that can be used.  The *ancdata* argument specifies the ancillary
1043   data (control messages) as an iterable of zero or more tuples
1044   ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and
1045   *cmsg_type* are integers specifying the protocol level and
1046   protocol-specific type respectively, and *cmsg_data* is a
1047   buffer-compatible object holding the associated data.  Note that
1048   some systems (in particular, systems without :func:`CMSG_SPACE`)
1049   might support sending only one control message per call.  The
1050   *flags* argument defaults to 0 and has the same meaning as for
1051   :meth:`send`.  If *address* is supplied and not ``None``, it sets a
1052   destination address for the message.  The return value is the
1053   number of bytes of non-ancillary data sent.
1054
1055   The following function sends the list of file descriptors *fds*
1056   over an :const:`AF_UNIX` socket, on systems which support the
1057   :const:`SCM_RIGHTS` mechanism.  See also :meth:`recvmsg`. ::
1058
1059      import socket, array
1060
1061      def send_fds(sock, msg, fds):
1062          return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])
1063
1064   Availability: most Unix platforms, possibly others.
1065
1066   .. versionadded:: 3.3
1067
1068
1069.. method:: socket.setblocking(flag)
1070
1071   Set blocking or non-blocking mode of the socket: if *flag* is false, the
1072   socket is set to non-blocking, else to blocking mode.
1073
1074   This method is a shorthand for certain :meth:`~socket.settimeout` calls:
1075
1076   * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)``
1077
1078   * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)``
1079
1080
1081.. method:: socket.settimeout(value)
1082
1083   Set a timeout on blocking socket operations.  The *value* argument can be a
1084   nonnegative floating point number expressing seconds, or ``None``.
1085   If a non-zero value is given, subsequent socket operations will raise a
1086   :exc:`timeout` exception if the timeout period *value* has elapsed before
1087   the operation has completed.  If zero is given, the socket is put in
1088   non-blocking mode. If ``None`` is given, the socket is put in blocking mode.
1089
1090   For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`.
1091
1092
1093.. method:: socket.setsockopt(level, optname, value)
1094
1095   .. index:: module: struct
1096
1097   Set the value of the given socket option (see the Unix manual page
1098   :manpage:`setsockopt(2)`).  The needed symbolic constants are defined in the
1099   :mod:`socket` module (:const:`SO_\*` etc.).  The value can be an integer or a
1100   bytes object representing a buffer.  In the latter case it is up to the caller to
1101   ensure that the bytestring contains the proper bits (see the optional built-in
1102   module :mod:`struct` for a way to encode C structures as bytestrings).
1103
1104
1105.. method:: socket.shutdown(how)
1106
1107   Shut down one or both halves of the connection.  If *how* is :const:`SHUT_RD`,
1108   further receives are disallowed.  If *how* is :const:`SHUT_WR`, further sends
1109   are disallowed.  If *how* is :const:`SHUT_RDWR`, further sends and receives are
1110   disallowed.
1111
1112
1113.. method:: socket.share(process_id)
1114
1115    :platform: Windows
1116
1117    Duplacet a socket and prepare it for sharing with a target process.  The
1118    target process must be provided with *process_id*.  The resulting bytes object
1119    can then be passed to the target process using some form of interprocess
1120    communication and the socket can be recreated there using :func:`fromshare`.
1121    Once this method has been called, it is safe to close the socket since
1122    the operating system has already duplicated it for the target process.
1123
1124   .. versionadded:: 3.3
1125
1126
1127Note that there are no methods :meth:`read` or :meth:`write`; use
1128:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead.
1129
1130Socket objects also have these (read-only) attributes that correspond to the
1131values given to the :class:`socket` constructor.
1132
1133
1134.. attribute:: socket.family
1135
1136   The socket family.
1137
1138
1139.. attribute:: socket.type
1140
1141   The socket type.
1142
1143
1144.. attribute:: socket.proto
1145
1146   The socket protocol.
1147
1148
1149
1150.. _socket-timeouts:
1151
1152Notes on socket timeouts
1153------------------------
1154
1155A socket object can be in one of three modes: blocking, non-blocking, or
1156timeout.  Sockets are by default always created in blocking mode, but this
1157can be changed by calling :func:`setdefaulttimeout`.
1158
1159* In *blocking mode*, operations block until complete or the system returns
1160  an error (such as connection timed out).
1161
1162* In *non-blocking mode*, operations fail (with an error that is unfortunately
1163  system-dependent) if they cannot be completed immediately: functions from the
1164  :mod:`select` can be used to know when and whether a socket is available for
1165  reading or writing.
1166
1167* In *timeout mode*, operations fail if they cannot be completed within the
1168  timeout specified for the socket (they raise a :exc:`timeout` exception)
1169  or if the system returns an error.
1170
1171.. note::
1172   At the operating system level, sockets in *timeout mode* are internally set
1173   in non-blocking mode.  Also, the blocking and timeout modes are shared between
1174   file descriptors and socket objects that refer to the same network endpoint.
1175   This implementation detail can have visible consequences if e.g. you decide
1176   to use the :meth:`~socket.fileno()` of a socket.
1177
1178Timeouts and the ``connect`` method
1179^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1180
1181The :meth:`~socket.connect` operation is also subject to the timeout
1182setting, and in general it is recommended to call :meth:`~socket.settimeout`
1183before calling :meth:`~socket.connect` or pass a timeout parameter to
1184:meth:`create_connection`.  However, the system network stack may also
1185return a connection timeout error of its own regardless of any Python socket
1186timeout setting.
1187
1188Timeouts and the ``accept`` method
1189^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1190
1191If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by
1192the :meth:`~socket.accept` method inherit that timeout.  Otherwise, the
1193behaviour depends on settings of the listening socket:
1194
1195* if the listening socket is in *blocking mode* or in *timeout mode*,
1196  the socket returned by :meth:`~socket.accept` is in *blocking mode*;
1197
1198* if the listening socket is in *non-blocking mode*, whether the socket
1199  returned by :meth:`~socket.accept` is in blocking or non-blocking mode
1200  is operating system-dependent.  If you want to ensure cross-platform
1201  behaviour, it is recommended you manually override this setting.
1202
1203
1204.. _socket-example:
1205
1206Example
1207-------
1208
1209Here are four minimal example programs using the TCP/IP protocol: a server that
1210echoes all data that it receives back (servicing only one client), and a client
1211using it.  Note that a server must perform the sequence :func:`socket`,
1212:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly
1213repeating the :meth:`~socket.accept` to service more than one client), while a
1214client only needs the sequence :func:`socket`, :meth:`~socket.connect`.  Also
1215note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on
1216the socket it is listening on but on the new socket returned by
1217:meth:`~socket.accept`.
1218
1219The first two examples support IPv4 only. ::
1220
1221   # Echo server program
1222   import socket
1223
1224   HOST = ''                 # Symbolic name meaning all available interfaces
1225   PORT = 50007              # Arbitrary non-privileged port
1226   s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
1227   s.bind((HOST, PORT))
1228   s.listen(1)
1229   conn, addr = s.accept()
1230   print('Connected by', addr)
1231   while True:
1232       data = conn.recv(1024)
1233       if not data: break
1234       conn.sendall(data)
1235   conn.close()
1236
1237::
1238
1239   # Echo client program
1240   import socket
1241
1242   HOST = 'daring.cwi.nl'    # The remote host
1243   PORT = 50007              # The same port as used by the server
1244   s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
1245   s.connect((HOST, PORT))
1246   s.sendall(b'Hello, world')
1247   data = s.recv(1024)
1248   s.close()
1249   print('Received', repr(data))
1250
1251The next two examples are identical to the above two, but support both IPv4 and
1252IPv6. The server …

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