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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  :const:`AF_CAN`) 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.. data:: CAN_BCM
 261          CAN_BCM_*
 262
 263   CAN_BCM, in the CAN protocol family, is the broadcast manager (BCM) protocol.
 264   Broadcast manager constants, documented in the Linux documentation, are also
 265   defined in the socket module.
 266
 267   Availability: Linux >= 2.6.25.
 268
 269   .. versionadded:: 3.4
 270
 271.. data:: AF_RDS
 272          PF_RDS
 273          SOL_RDS
 274          RDS_*
 275
 276   Many constants of these forms, documented in the Linux documentation, are
 277   also defined in the socket module.
 278
 279   Availability: Linux >= 2.6.30.
 280
 281   .. versionadded:: 3.3
 282
 283
 284.. data:: SIO_*
 285          RCVALL_*
 286
 287   Constants for Windows' WSAIoctl(). The constants are used as arguments to the
 288   :meth:`ioctl` method of socket objects.
 289
 290
 291.. data:: TIPC_*
 292
 293   TIPC related constants, matching the ones exported by the C socket API. See
 294   the TIPC documentation for more information.
 295
 296.. data:: AF_LINK
 297
 298  Availability: BSD, OSX.
 299
 300  .. versionadded:: 3.4
 301
 302.. data:: has_ipv6
 303
 304   This constant contains a boolean value which indicates if IPv6 is supported on
 305   this platform.
 306
 307
 308.. function:: create_connection(address[, timeout[, source_address]])
 309
 310   Connect to a TCP service listening on the Internet *address* (a 2-tuple
 311   ``(host, port)``), and return the socket object.  This is a higher-level
 312   function than :meth:`socket.connect`: if *host* is a non-numeric hostname,
 313   it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`,
 314   and then try to connect to all possible addresses in turn until a
 315   connection succeeds.  This makes it easy to write clients that are
 316   compatible to both IPv4 and IPv6.
 317
 318   Passing the optional *timeout* parameter will set the timeout on the
 319   socket instance before attempting to connect.  If no *timeout* is
 320   supplied, the global default timeout setting returned by
 321   :func:`getdefaulttimeout` is used.
 322
 323   If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the
 324   socket to bind to as its source address before connecting.  If host or port
 325   are '' or 0 respectively the OS default behavior will be used.
 326
 327   .. versionchanged:: 3.2
 328      *source_address* was added.
 329
 330   .. versionchanged:: 3.2
 331      support for the :keyword:`with` statement was added.
 332
 333
 334.. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0)
 335
 336   Translate the *host*/*port* argument into a sequence of 5-tuples that contain
 337   all the necessary arguments for creating a socket connected to that service.
 338   *host* is a domain name, a string representation of an IPv4/v6 address
 339   or ``None``. *port* is a string service name such as ``'http'``, a numeric
 340   port number or ``None``.  By passing ``None`` as the value of *host*
 341   and *port*, you can pass ``NULL`` to the underlying C API.
 342
 343   The *family*, *type* and *proto* arguments can be optionally specified
 344   in order to narrow the list of addresses returned.  Passing zero as a
 345   value for each of these arguments selects the full range of results.
 346   The *flags* argument can be one or several of the ``AI_*`` constants,
 347   and will influence how results are computed and returned.
 348   For example, :const:`AI_NUMERICHOST` will disable domain name resolution
 349   and will raise an error if *host* is a domain name.
 350
 351   The function returns a list of 5-tuples with the following structure:
 352
 353   ``(family, type, proto, canonname, sockaddr)``
 354
 355   In these tuples, *family*, *type*, *proto* are all integers and are
 356   meant to be passed to the :func:`.socket` function.  *canonname* will be
 357   a string representing the canonical name of the *host* if
 358   :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname*
 359   will be empty.  *sockaddr* is a tuple describing a socket address, whose
 360   format depends on the returned *family* (a ``(address, port)`` 2-tuple for
 361   :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for
 362   :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect`
 363   method.
 364
 365   The following example fetches address information for a hypothetical TCP
 366   connection to ``www.python.org`` on port 80 (results may differ on your
 367   system if IPv6 isn't enabled)::
 368
 369      >>> socket.getaddrinfo("www.python.org", 80, proto=socket.SOL_TCP)
 370      [(2, 1, 6, '', ('82.94.164.162', 80)),
 371       (10, 1, 6, '', ('2001:888:2000:d::a2', 80, 0, 0))]
 372
 373   .. versionchanged:: 3.2
 374      parameters can now be passed as single keyword arguments.
 375
 376.. function:: getfqdn([name])
 377
 378   Return a fully qualified domain name for *name*. If *name* is omitted or empty,
 379   it is interpreted as the local host.  To find the fully qualified name, the
 380   hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the
 381   host, if available.  The first name which includes a period is selected.  In
 382   case no fully qualified domain name is available, the hostname as returned by
 383   :func:`gethostname` is returned.
 384
 385
 386.. function:: gethostbyname(hostname)
 387
 388   Translate a host name to IPv4 address format.  The IPv4 address is returned as a
 389   string, such as  ``'100.50.200.5'``.  If the host name is an IPv4 address itself
 390   it is returned unchanged.  See :func:`gethostbyname_ex` for a more complete
 391   interface. :func:`gethostbyname` does not support IPv6 name resolution, and
 392   :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support.
 393
 394
 395.. function:: gethostbyname_ex(hostname)
 396
 397   Translate a host name to IPv4 address format, extended interface. Return a
 398   triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary
 399   host name responding to the given *ip_address*, *aliaslist* is a (possibly
 400   empty) list of alternative host names for the same address, and *ipaddrlist* is
 401   a list of IPv4 addresses for the same interface on the same host (often but not
 402   always a single address). :func:`gethostbyname_ex` does not support IPv6 name
 403   resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual
 404   stack support.
 405
 406
 407.. function:: gethostname()
 408
 409   Return a string containing the hostname of the machine where  the Python
 410   interpreter is currently executing.
 411
 412   If you want to know the current machine's IP address, you may want to use
 413   ``gethostbyname(gethostname())``. This operation assumes that there is a
 414   valid address-to-host mapping for the host, and the assumption does not
 415   always hold.
 416
 417   Note: :func:`gethostname` doesn't always return the fully qualified domain
 418   name; use ``getfqdn()`` (see above).
 419
 420
 421.. function:: gethostbyaddr(ip_address)
 422
 423   Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the
 424   primary host name responding to the given *ip_address*, *aliaslist* is a
 425   (possibly empty) list of alternative host names for the same address, and
 426   *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same
 427   host (most likely containing only a single address). To find the fully qualified
 428   domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports
 429   both IPv4 and IPv6.
 430
 431
 432.. function:: getnameinfo(sockaddr, flags)
 433
 434   Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending
 435   on the settings of *flags*, the result can contain a fully-qualified domain name
 436   or numeric address representation in *host*.  Similarly, *port* can contain a
 437   string port name or a numeric port number.
 438
 439
 440.. function:: getprotobyname(protocolname)
 441
 442   Translate an Internet protocol name (for example, ``'icmp'``) to a constant
 443   suitable for passing as the (optional) third argument to the :func:`.socket`
 444   function.  This is usually only needed for sockets opened in "raw" mode
 445   (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen
 446   automatically if the protocol is omitted or zero.
 447
 448
 449.. function:: getservbyname(servicename[, protocolname])
 450
 451   Translate an Internet service name and protocol name to a port number for that
 452   service.  The optional protocol name, if given, should be ``'tcp'`` or
 453   ``'udp'``, otherwise any protocol will match.
 454
 455
 456.. function:: getservbyport(port[, protocolname])
 457
 458   Translate an Internet port number and protocol name to a service name for that
 459   service.  The optional protocol name, if given, should be ``'tcp'`` or
 460   ``'udp'``, otherwise any protocol will match.
 461
 462
 463.. function:: socket([family[, type[, proto]]])
 464
 465   Create a new socket using the given address family, socket type and protocol
 466   number.  The address family should be :const:`AF_INET` (the default),
 467   :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The
 468   socket type should be :const:`SOCK_STREAM` (the default),
 469   :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_``
 470   constants. The protocol number is usually zero and may be omitted or in the
 471   case where the address family is :const:`AF_CAN` the protocol should be one
 472   of :const:`CAN_RAW` or :const:`CAN_BCM`.
 473
 474   .. versionchanged:: 3.3
 475      The AF_CAN family was added.
 476      The AF_RDS family was added.
 477
 478  .. versionchanged:: 3.4
 479      The CAN_BCM protocol was added.
 480
 481.. function:: socketpair([family[, type[, proto]]])
 482
 483   Build a pair of connected socket objects using the given address family, socket
 484   type, and protocol number.  Address family, socket type, and protocol number are
 485   as for the :func:`.socket` function above. The default family is :const:`AF_UNIX`
 486   if defined on the platform; otherwise, the default is :const:`AF_INET`.
 487   Availability: Unix.
 488
 489   .. versionchanged:: 3.2
 490      The returned socket objects now support the whole socket API, rather
 491      than a subset.
 492
 493
 494.. function:: fromfd(fd, family, type[, proto])
 495
 496   Duplicate the file descriptor *fd* (an integer as returned by a file object's
 497   :meth:`fileno` method) and build a socket object from the result.  Address
 498   family, socket type and protocol number are as for the :func:`.socket` function
 499   above. The file descriptor should refer to a socket, but this is not checked ---
 500   subsequent operations on the object may fail if the file descriptor is invalid.
 501   This function is rarely needed, but can be used to get or set socket options on
 502   a socket passed to a program as standard input or output (such as a server
 503   started by the Unix inet daemon).  The socket is assumed to be in blocking mode.
 504
 505
 506.. function:: ntohl(x)
 507
 508   Convert 32-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 4-byte swap operation.
 511
 512
 513.. function:: ntohs(x)
 514
 515   Convert 16-bit positive integers from network to host 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 2-byte swap operation.
 518
 519
 520.. function:: htonl(x)
 521
 522   Convert 32-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 4-byte swap operation.
 525
 526
 527.. function:: htons(x)
 528
 529   Convert 16-bit positive integers from host to network byte order.  On machines
 530   where the host byte order is the same as network byte order, this is a no-op;
 531   otherwise, it performs a 2-byte swap operation.
 532
 533
 534.. function:: inet_aton(ip_string)
 535
 536   Convert an IPv4 address from dotted-quad string format (for example,
 537   '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in
 538   length.  This is useful when conversing with a program that uses the standard C
 539   library and needs objects of type :c:type:`struct in_addr`, which is the C type
 540   for the 32-bit packed binary this function returns.
 541
 542   :func:`inet_aton` also accepts strings with less than three dots; see the
 543   Unix manual page :manpage:`inet(3)` for details.
 544
 545   If the IPv4 address string passed to this function is invalid,
 546   :exc:`OSError` will be raised. Note that exactly what is valid depends on
 547   the underlying C implementation of :c:func:`inet_aton`.
 548
 549   :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used
 550   instead for IPv4/v6 dual stack support.
 551
 552
 553.. function:: inet_ntoa(packed_ip)
 554
 555   Convert a 32-bit packed IPv4 address (a bytes object four characters in
 556   length) to its standard dotted-quad string representation (for example,
 557   '123.45.67.89').  This is useful when conversing with a program that uses the
 558   standard C library and needs objects of type :c:type:`struct in_addr`, which
 559   is the C type for the 32-bit packed binary data this function takes as an
 560   argument.
 561
 562   If the byte sequence passed to this function is not exactly 4 bytes in
 563   length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not
 564   support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual
 565   stack support.
 566
 567
 568.. function:: inet_pton(address_family, ip_string)
 569
 570   Convert an IP address from its family-specific string format to a packed,
 571   binary format. :func:`inet_pton` is useful when a library or network protocol
 572   calls for an object of type :c:type:`struct in_addr` (similar to
 573   :func:`inet_aton`) or :c:type:`struct in6_addr`.
 574
 575   Supported values for *address_family* are currently :const:`AF_INET` and
 576   :const:`AF_INET6`. If the IP address string *ip_string* is invalid,
 577   :exc:`OSError` will be raised. Note that exactly what is valid depends on
 578   both the value of *address_family* and the underlying implementation of
 579   :c:func:`inet_pton`.
 580
 581   Availability: Unix (maybe not all platforms).
 582
 583
 584.. function:: inet_ntop(address_family, packed_ip)
 585
 586   Convert a packed IP address (a bytes object of some number of characters) to its
 587   standard, family-specific string representation (for example, ``'7.10.0.5'`` or
 588   ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol
 589   returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`)
 590   or :c:type:`struct in6_addr`.
 591
 592   Supported values for *address_family* are currently :const:`AF_INET` and
 593   :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the
 594   specified address family, :exc:`ValueError` will be raised.  A
 595   :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`.
 596
 597   Availability: Unix (maybe not all platforms).
 598
 599
 600..
 601   XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any
 602   non-Unix platforms?  The old (obsolete?) 4.2BSD form of the
 603   interface, in which struct msghdr has no msg_control or
 604   msg_controllen members, is not currently supported.
 605
 606.. function:: CMSG_LEN(length)
 607
 608   Return the total length, without trailing padding, of an ancillary
 609   data item with associated data of the given *length*.  This value
 610   can often be used as the buffer size for :meth:`~socket.recvmsg` to
 611   receive a single item of ancillary data, but :rfc:`3542` requires
 612   portable applications to use :func:`CMSG_SPACE` and thus include
 613   space for padding, even when the item will be the last in the
 614   buffer.  Raises :exc:`OverflowError` if *length* is outside the
 615   permissible range of values.
 616
 617   Availability: most Unix platforms, possibly others.
 618
 619   .. versionadded:: 3.3
 620
 621
 622.. function:: CMSG_SPACE(length)
 623
 624   Return the buffer size needed for :meth:`~socket.recvmsg` to
 625   receive an ancillary data item with associated data of the given
 626   *length*, along with any trailing padding.  The buffer space needed
 627   to receive multiple items is the sum of the :func:`CMSG_SPACE`
 628   values for their associated data lengths.  Raises
 629   :exc:`OverflowError` if *length* is outside the permissible range
 630   of values.
 631
 632   Note that some systems might support ancillary data without
 633   providing this function.  Also note that setting the buffer size
 634   using the results of this function may not precisely limit the
 635   amount of ancillary data that can be received, since additional
 636   data may be able to fit into the padding area.
 637
 638   Availability: most Unix platforms, possibly others.
 639
 640   .. versionadded:: 3.3
 641
 642
 643.. function:: getdefaulttimeout()
 644
 645   Return the default timeout in seconds (float) for new socket objects. A value
 646   of ``None`` indicates that new socket objects have no timeout. When the socket
 647   module is first imported, the default is ``None``.
 648
 649
 650.. function:: setdefaulttimeout(timeout)
 651
 652   Set the default timeout in seconds (float) for new socket objects.  When
 653   the socket module is first imported, the default is ``None``.  See
 654   :meth:`~socket.settimeout` for possible values and their respective
 655   meanings.
 656
 657
 658.. function:: sethostname(name)
 659
 660   Set the machine's hostname to *name*.  This will raise a
 661   :exc:`OSError` if you don't have enough rights.
 662
 663   Availability: Unix.
 664
 665   .. versionadded:: 3.3
 666
 667
 668.. function:: if_nameindex()
 669
 670   Return a list of network interface information
 671   (index int, name string) tuples.
 672   :exc:`OSError` if the system call fails.
 673
 674   Availability: Unix.
 675
 676   .. versionadded:: 3.3
 677
 678
 679.. function:: if_nametoindex(if_name)
 680
 681   Return a network interface index number corresponding to an
 682   interface name.
 683   :exc:`OSError` if no interface with the given name exists.
 684
 685   Availability: Unix.
 686
 687   .. versionadded:: 3.3
 688
 689
 690.. function:: if_indextoname(if_index)
 691
 692   Return a network interface name corresponding to a
 693   interface index number.
 694   :exc:`OSError` if no interface with the given index exists.
 695
 696   Availability: Unix.
 697
 698   .. versionadded:: 3.3
 699
 700
 701.. function:: fromshare(data)
 702
 703   Instantiate a socket from data obtained from :meth:`~socket.share`.
 704   The socket is assumed to be in blocking mode.
 705
 706   Availability: Windows.
 707
 708   .. versionadded:: 3.3
 709
 710
 711.. data:: SocketType
 712
 713   This is a Python type object that represents the socket object type. It is the
 714   same as ``type(socket(...))``.
 715
 716
 717.. _socket-objects:
 718
 719Socket Objects
 720--------------
 721
 722Socket objects have the following methods.  Except for :meth:`makefile` these
 723correspond to Unix system calls applicable to sockets.
 724
 725
 726.. method:: socket.accept()
 727
 728   Accept a connection. The socket must be bound to an address and listening for
 729   connections. The return value is a pair ``(conn, address)`` where *conn* is a
 730   *new* socket object usable to send and receive data on the connection, and
 731   *address* is the address bound to the socket on the other end of the connection.
 732
 733
 734.. method:: socket.bind(address)
 735
 736   Bind the socket to *address*.  The socket must not already be bound. (The format
 737   of *address* depends on the address family --- see above.)
 738
 739
 740.. method:: socket.close()
 741
 742   Close the socket.  All future operations on the socket object will fail. The
 743   remote end will receive no more data (after queued data is flushed). Sockets are
 744   automatically closed when they are garbage-collected.
 745
 746   .. note::
 747      :meth:`close()` releases the resource associated with a connection but
 748      does not necessarily close the connection immediately.  If you want
 749      to close the connection in a timely fashion, call :meth:`shutdown()`
 750      before :meth:`close()`.
 751
 752
 753.. method:: socket.connect(address)
 754
 755   Connect to a remote socket at *address*. (The format of *address* depends on the
 756   address family --- see above.)
 757
 758
 759.. method:: socket.connect_ex(address)
 760
 761   Like ``connect(address)``, but return an error indicator instead of raising an
 762   exception for errors returned by the C-level :c:func:`connect` call (other
 763   problems, such as "host not found," can still raise exceptions).  The error
 764   indicator is ``0`` if the operation succeeded, otherwise the value of the
 765   :c:data:`errno` variable.  This is useful to support, for example, asynchronous
 766   connects.
 767
 768
 769.. method:: socket.detach()
 770
 771   Put the socket object into closed state without actually closing the
 772   underlying file descriptor.  The file descriptor is returned, and can
 773   be reused for other purposes.
 774
 775   .. versionadded:: 3.2
 776
 777
 778.. method:: socket.fileno()
 779
 780   Return the socket's file descriptor (a small integer).  This is useful with
 781   :func:`select.select`.
 782
 783   Under Windows the small integer returned by this method cannot be used where a
 784   file descriptor can be used (such as :func:`os.fdopen`).  Unix does not have
 785   this limitation.
 786
 787
 788.. method:: socket.getpeername()
 789
 790   Return the remote address to which the socket is connected.  This is useful to
 791   find out the port number of a remote IPv4/v6 socket, for instance. (The format
 792   of the address returned depends on the address family --- see above.)  On some
 793   systems this function is not supported.
 794
 795
 796.. method:: socket.getsockname()
 797
 798   Return the socket's own address.  This is useful to find out the port number of
 799   an IPv4/v6 socket, for instance. (The format of the address returned depends on
 800   the address family --- see above.)
 801
 802
 803.. method:: socket.getsockopt(level, optname[, buflen])
 804
 805   Return the value of the given socket option (see the Unix man page
 806   :manpage:`getsockopt(2)`).  The needed symbolic constants (:const:`SO_\*` etc.)
 807   are defined in this module.  If *buflen* is absent, an integer option is assumed
 808   and its integer value is returned by the function.  If *buflen* is present, it
 809   specifies the maximum length of the buffer used to receive the option in, and
 810   this buffer is returned as a bytes object.  It is up to the caller to decode the
 811   contents of the buffer (see the optional built-in module :mod:`struct` for a way
 812   to decode C structures encoded as byte strings).
 813
 814
 815.. method:: socket.gettimeout()
 816
 817   Return the timeout in seconds (float) associated with socket operations,
 818   or ``None`` if no timeout is set.  This reflects the last call to
 819   :meth:`setblocking` or :meth:`settimeout`.
 820
 821
 822.. method:: socket.ioctl(control, option)
 823
 824   :platform: Windows
 825
 826   The :meth:`ioctl` method is a limited interface to the WSAIoctl system
 827   interface.  Please refer to the `Win32 documentation
 828   <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more
 829   information.
 830
 831   On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl`
 832   functions may be used; they accept a socket object as their first argument.
 833
 834.. method:: socket.listen(backlog)
 835
 836   Listen for connections made to the socket.  The *backlog* argument specifies the
 837   maximum number of queued connections and should be at least 0; the maximum value
 838   is system-dependent (usually 5), the minimum value is forced to 0.
 839
 840
 841.. method:: socket.makefile(mode='r', buffering=None, *, encoding=None, \
 842                            errors=None, newline=None)
 843
 844   .. index:: single: I/O control; buffering
 845
 846   Return a :term:`file object` associated with the socket.  The exact returned
 847   type depends on the arguments given to :meth:`makefile`.  These arguments are
 848   interpreted the same way as by the built-in :func:`open` function.
 849
 850   Closing the file object won't close the socket unless there are no remaining
 851   references to the socket.  The socket must be in blocking mode; it can have
 852   a timeout, but the file object's internal buffer may end up in a inconsistent
 853   state if a timeout occurs.
 854
 855   .. note::
 856
 857      On Windows, the file-like object created by :meth:`makefile` cannot be
 858      used where a file object with a file descriptor is expected, such as the
 859      stream arguments of :meth:`subprocess.Popen`.
 860
 861
 862.. method:: socket.recv(bufsize[, flags])
 863
 864   Receive data from the socket.  The return value is a bytes object representing the
 865   data received.  The maximum amount of data to be received at once is specified
 866   by *bufsize*.  See the Unix manual page :manpage:`recv(2)` for the meaning of
 867   the optional argument *flags*; it defaults to zero.
 868
 869   .. note::
 870
 871      For best match with hardware and network realities, the value of  *bufsize*
 872      should be a relatively small power of 2, for example, 4096.
 873
 874
 875.. method:: socket.recvfrom(bufsize[, flags])
 876
 877   Receive data from the socket.  The return value is a pair ``(bytes, address)``
 878   where *bytes* is a bytes object representing the data received and *address* is the
 879   address of the socket sending the data.  See the Unix manual page
 880   :manpage:`recv(2)` for the meaning of the optional argument *flags*; it defaults
 881   to zero. (The format of *address* depends on the address family --- see above.)
 882
 883
 884.. method:: socket.recvmsg(bufsize[, ancbufsize[, flags]])
 885
 886   Receive normal data (up to *bufsize* bytes) and ancillary data from
 887   the socket.  The *ancbufsize* argument sets the size in bytes of
 888   the internal buffer used to receive the ancillary data; it defaults
 889   to 0, meaning that no ancillary data will be received.  Appropriate
 890   buffer sizes for ancillary data can be calculated using
 891   :func:`CMSG_SPACE` or :func:`CMSG_LEN`, and items which do not fit
 892   into the buffer might be truncated or discarded.  The *flags*
 893   argument defaults to 0 and has the same meaning as for
 894   :meth:`recv`.
 895
 896   The return value is a 4-tuple: ``(data, ancdata, msg_flags,
 897   address)``.  The *data* item is a :class:`bytes` object holding the
 898   non-ancillary data received.  The *ancdata* item is a list of zero
 899   or more tuples ``(cmsg_level, cmsg_type, cmsg_data)`` representing
 900   the ancillary data (control messages) received: *cmsg_level* and
 901   *cmsg_type* are integers specifying the protocol level and
 902   protocol-specific type respectively, and *cmsg_data* is a
 903   :class:`bytes` object holding the associated data.  The *msg_flags*
 904   item is the bitwise OR of various flags indicating conditions on
 905   the received message; see your system documentation for details.
 906   If the receiving socket is unconnected, *address* is the address of
 907   the sending socket, if available; otherwise, its value is
 908   unspecified.
 909
 910   On some systems, :meth:`sendmsg` and :meth:`recvmsg` can be used to
 911   pass file descriptors between processes over an :const:`AF_UNIX`
 912   socket.  When this facility is used (it is often restricted to
 913   :const:`SOCK_STREAM` sockets), :meth:`recvmsg` will return, in its
 914   ancillary data, items of the form ``(socket.SOL_SOCKET,
 915   socket.SCM_RIGHTS, fds)``, where *fds* is a :class:`bytes` object
 916   representing the new file descriptors as a binary array of the
 917   native C :c:type:`int` type.  If :meth:`recvmsg` raises an
 918   exception after the system call returns, it will first attempt to
 919   close any file descriptors received via this mechanism.
 920
 921   Some systems do not indicate the truncated length of ancillary data
 922   items which have been only partially received.  If an item appears
 923   to extend beyond the end of the buffer, :meth:`recvmsg` will issue
 924   a :exc:`RuntimeWarning`, and will return the part of it which is
 925   inside the buffer provided it has not been truncated before the
 926   start of its associated data.
 927
 928   On systems which support the :const:`SCM_RIGHTS` mechanism, the
 929   following function will receive up to *maxfds* file descriptors,
 930   returning the message data and a list containing the descriptors
 931   (while ignoring unexpected conditions such as unrelated control
 932   messages being received).  See also :meth:`sendmsg`. ::
 933
 934      import socket, array
 935
 936      def recv_fds(sock, msglen, maxfds):
 937          fds = array.array("i")   # Array of ints
 938          msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
 939          for cmsg_level, cmsg_type, cmsg_data in ancdata:
 940              if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
 941                  # Append data, ignoring any truncated integers at the end.
 942                  fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
 943          return msg, list(fds)
 944
 945   Availability: most Unix platforms, possibly others.
 946
 947   .. versionadded:: 3.3
 948
 949
 950.. method:: socket.recvmsg_into(buffers[, ancbufsize[, flags]])
 951
 952   Receive normal data and ancillary data from the socket, behaving as
 953   :meth:`recvmsg` would, but scatter the non-ancillary data into a
 954   series of buffers instead of returning a new bytes object.  The
 955   *buffers* argument must be an iterable of objects that export
 956   writable buffers (e.g. :class:`bytearray` objects); these will be
 957   filled with successive chunks of the non-ancillary data until it
 958   has all been written or there are no more buffers.  The operating
 959   system may set a limit (:func:`~os.sysconf` value ``SC_IOV_MAX``)
 960   on the number of buffers that can be used.  The *ancbufsize* and
 961   *flags* arguments have the same meaning as for :meth:`recvmsg`.
 962
 963   The return value is a 4-tuple: ``(nbytes, ancdata, msg_flags,
 964   address)``, where *nbytes* is the total number of bytes of
 965   non-ancillary data written into the buffers, and *ancdata*,
 966   *msg_flags* and *address* are the same as for :meth:`recvmsg`.
 967
 968   Example::
 969
 970      >>> import socket
 971      >>> s1, s2 = socket.socketpair()
 972      >>> b1 = bytearray(b'----')
 973      >>> b2 = bytearray(b'0123456789')
 974      >>> b3 = bytearray(b'--------------')
 975      >>> s1.send(b'Mary had a little lamb')
 976      22
 977      >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3])
 978      (22, [], 0, None)
 979      >>> [b1, b2, b3]
 980      [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')]
 981
 982   Availability: most Unix platforms, possibly others.
 983
 984   .. versionadded:: 3.3
 985
 986
 987.. method:: socket.recvfrom_into(buffer[, nbytes[, flags]])
 988
 989   Receive data from the socket, writing it into *buffer* instead of creating a
 990   new bytestring.  The return value is a pair ``(nbytes, address)`` where *nbytes* is
 991   the number of bytes received and *address* is the address of the socket sending
 992   the data.  See the Unix manual page :manpage:`recv(2)` for the meaning of the
 993   optional argument *flags*; it defaults to zero.  (The format of *address*
 994   depends on the address family --- see above.)
 995
 996
 997.. method:: socket.recv_into(buffer[, nbytes[, flags]])
 998
 999   Receive up to *nbytes* bytes from the socket, storing the data into a buffer
1000   rather than creating a new bytestring.  If *nbytes* is not specified (or 0),
1001   receive up to the size available in the given buffer.  Returns the number of
1002   bytes received.  See the Unix manual page :manpage:`recv(2)` for the meaning
1003   of the optional argument *flags*; it defaults to zero.
1004
1005
1006.. method:: socket.send(bytes[, flags])
1007
1008   Send data to the socket.  The socket must be connected to a remote socket.  The
1009   optional *flags* argument has the same meaning as for :meth:`recv` above.
1010   Returns the number of bytes sent. Applications are responsible for checking that
1011   all data has been sent; if only some of the data was transmitted, the
1012   application needs to attempt delivery of the remaining data. For further
1013   information on this topic, consult the :ref:`socket-howto`.
1014
1015
1016.. method:: socket.sendall(bytes[, flags])
1017
1018   Send data to the socket.  The socket must be connected to a remote socket.  The
1019   optional *flags* argument has the same meaning as for :meth:`recv` above.
1020   Unlike :meth:`send`, this method continues to send data from *bytes* until
1021   either all data has been sent or an error occurs.  ``None`` is returned on
1022   success.  On error, an exception is raised, and there is no way to determine how
1023   much data, if any, was successfully sent.
1024
1025
1026.. method:: socket.sendto(bytes, address)
1027            socket.sendto(bytes, flags, address)
1028
1029   Send data to the socket.  The socket should not be connected to a remote socket,
1030   since the destination socket is specified by *address*.  The optional *flags*
1031   argument has the same meaning as for :meth:`recv` above.  Return the number of
1032   bytes sent. (The format of *address* depends on the address family --- see
1033   above.)
1034
1035
1036.. method:: socket.sendmsg(buffers[, ancdata[, flags[, address]]])
1037
1038   Send normal and ancillary data to the socket, gathering the
1039   non-ancillary data from a series of buffers and concatenating it
1040   into a single message.  The *buffers* argument specifies the
1041   non-ancillary data as an iterable of buffer-compatible objects
1042   (e.g. :class:`bytes` objects); the operating system may set a limit
1043   (:func:`~os.sysconf` value ``SC_IOV_MAX``) on the number of buffers
1044   that can be used.  The *ancdata* argument specifies the ancillary
1045   data (control messages) as an iterable of zero or more tuples
1046   ``(cmsg_level, cmsg_type, cmsg_data)``, where *cmsg_level* and
1047   *cmsg_type* are integers specifying the protocol level and
1048   protocol-specific type respectively, and *cmsg_data* is a
1049   buffer-compatible object holding the associated data.  Note that
1050   some systems (in particular, systems without :func:`CMSG_SPACE`)
1051   might support sending only one control message per call.  The
1052   *flags* argument defaults to 0 and has the same meaning as for
1053   :meth:`send`.  If *address* is supplied and not ``None``, it sets a
1054   destination address for the message.  The return value is the
1055   number of bytes of non-ancillary data sent.
1056
1057   The following function sends the list of file descriptors *fds*
1058   over an :const:`AF_UNIX` socket, on systems which support the
1059   :const:`SCM_RIGHTS` mechanism.  See also :meth:`recvmsg`. ::
1060
1061      import socket, array
1062
1063      def send_fds(sock, msg, fds):
1064          return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])
1065
1066   Availability: most Unix platforms, possibly others.
1067
1068   .. versionadded:: 3.3
1069
1070
1071.. method:: socket.setblocking(flag)
1072
1073   Set blocking or non-blocking mode of the socket: if *flag* is false, the
1074   socket is set to non-blocking, else to blocking mode.
1075
1076   This method is a shorthand for certain :meth:`~socket.settimeout` calls:
1077
1078   * ``sock.setblocking(True)`` is equivalent to ``sock.settimeout(None)``
1079
1080   * ``sock.setblocking(False)`` is equivalent to ``sock.settimeout(0.0)``
1081
1082
1083.. method:: socket.settimeout(value)
1084
1085   Set a timeout on blocking socket operations.  The *value* argument can be a
1086   nonnegative floating point number expressing seconds, or ``None``.
1087   If a non-zero value is given, subsequent socket operations will raise a
1088   :exc:`timeout` exception if the timeout period *value* has elapsed before
1089   the operation has completed.  If zero is given, the socket is put in
1090   non-blocking mode. If ``None`` is given, the socket is put in blocking mode.
1091
1092   For further information, please consult the :ref:`notes on socket timeouts <socket-timeouts>`.
1093
1094
1095.. method:: socket.setsockopt(level, optname, value)
1096
1097   .. index:: module: struct
1098
1099   Set the value of the given socket option (see the Unix manual page
1100   :manpage:`setsockopt(2)`).  The needed symbolic constants are defined in the
1101   :mod:`socket` module (:const:`SO_\*` etc.).  The value can be an integer or a
1102   bytes object representing a buffer.  In the latter case it is up to the caller to
1103   ensure that the bytestring contains the proper bits (see the optional built-in
1104   module :mod:`struct` for a way to encode C structures as bytestrings).
1105
1106
1107.. method:: socket.shutdown(how)
1108
1109   Shut down one or both halves of the connection.  If *how* is :const:`SHUT_RD`,
1110   further receives are disallowed.  If *how* is :const:`SHUT_WR`, further sends
1111   are disallowed.  If *how* is :const:`SHUT_RDWR`, further sends and receives are
1112   disallowed.
1113
1114
1115.. method:: socket.share(process_id)
1116
1117    :platform: Windows
1118
1119    Duplacet a socket and prepare it for sharing with a target process.  The
1120    target process must be provided with *process_id*.  The resulting bytes object
1121    can then be passed to the target process using some form of interprocess
1122    communication and the socket can be recreated there using :func:`fromshare`.
1123    Once this method has been called, it is safe to close the socket since
1124    the operating system has already duplicated it for the target process.
1125
1126   .. versionadded:: 3.3
1127
1128
1129Note that there are no methods :meth:`read` or :meth:`write`; use
1130:meth:`~socket.recv` and :meth:`~socket.send` without *flags* argument instead.
1131
1132Socket objects also have these (read-only) attributes that correspond to the
1133values given to the :class:`socket` constructor.
1134
1135
1136.. attribute:: socket.family
1137
1138   The socket family.
1139
1140
1141.. attribute:: socket.type
1142
1143   The socket type.
1144
1145
1146.. attribute:: socket.proto
1147
1148   The socket protocol.
1149
1150
1151
1152.. _socket-timeouts:
1153
1154Notes on socket timeouts
1155------------------------
1156
1157A socket object can be in one of three modes: blocking, non-blocking, or
1158timeout.  Sockets are by default always created in blocking mode, but this
1159can be changed by calling :func:`setdefaulttimeout`.
1160
1161* In *blocking mode*, operations block until complete or the system returns
1162  an error (such as connection timed out).
1163
1164* In *non-blocking mode*, operations fail (with an error that is unfortunately
1165  system-dependent) if they cannot be completed immediately: functions from the
1166  :mod:`select` can be used to know when and whether a socket is available for
1167  reading or writing.
1168
1169* In *timeout mode*, operations fail if they cannot be completed within the
1170  timeout specified for the socket (they raise a :exc:`timeout` exception)
1171  or if the system returns an error.
1172
1173.. note::
1174   At the operating system level, sockets in *timeout mode* are internally set
1175   in non-blocking mode.  Also, the blocking and timeout modes are shared between
1176   file descriptors and socket objects that refer to the same network endpoint.
1177   This implementation detail can have visible consequences if e.g. you decide
1178   to use the :meth:`~socket.fileno()` of a socket.
1179
1180Timeouts and the ``connect`` method
1181^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1182
1183The :meth:`~socket.connect` operation is also subject to the timeout
1184setting, and in general it is recommended to call :meth:`~socket.settimeout`
1185before calling :meth:`~socket.connect` or pass a timeout parameter to
1186:meth:`create_connection`.  However, the system network stack may also
1187return a connection timeout error of its own regardless of any Python socket
1188timeout setting.
1189
1190Timeouts and the ``accept`` method
1191^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1192
1193If :func:`getdefaulttimeout` is not :const:`None`, sockets returned by
1194the :meth:`~socket.accept` method inherit that timeout.  Otherwise, the
1195behaviour depends on settings of the listening socket:
1196
1197* if the listening socket is in *blocking mode* or in *timeout mode*,
1198  the socket returned by :meth:`~socket.accept` is in *blocking mode*;
1199
1200* if the listening socket is in *non-blocking mode*, whether the socket
1201  returned by :meth:`~socket.accept` is in blocking or non-blocking mode
1202  is operating system-dependent.  If you want to ensure cross-platform
1203  behaviour, it is recommended you manually override this setting.
1204
1205
1206.. _socket-example:
1207
1208Example
1209-------
1210
1211Here are four minimal example programs using the TCP/IP protocol: a server that
1212echoes all data that it receives back (servicing only one client), and a client
1213using it.  Note that a server must perform the sequence :func:`.socket`,
1214:meth:`~socket.bind`, :meth:`~socket.listen`, :meth:`~socket.accept` (possibly
1215repeating the :meth:`~socket.accept` to service more than one client), while a
1216client only needs the sequence :func:`.socket`, :meth:`~socket.connect`.  Also
1217note that the server does not :meth:`~socket.sendall`/:meth:`~socket.recv` on
1218the socket it is listening on but on the new socket returned by
1219:meth:`~socket.accept`.
1220
1221The first two examples support IPv4 only. ::
1222
1223   # Echo server program
1224   import socket
1225
1226   HOST = ''                 # Symbolic name meaning all available interfaces
1227   PORT = 50007              # Arbitrary non-privileged port
1228   s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
1229   s.bind((HOST, PORT))
1230   s.listen(1)
1231   conn, addr = s.accept()
1232   print('Connected by', addr)
1233   while True:
1234       data = conn.recv(1024)
1235       if not data: break
1236       conn.sendall(data)
1237   conn.close()
1238
1239::
1240
1241   # Echo client program
1242   import socket
1243
1244   HOST = 'daring.cwi.nl'    # The remote host
1245   PORT = 50007              # The same port as used by the server
1246   s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
1247   s.connect((HOST, PORT))
1248   s.sendall(b'Hello, world')
1249   data = s.recv(1024)
1250   s.close()
1251   print('Received', repr(data))
1252
1253The next two examples are identical to theā€¦

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