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:mod:`socket` --- Low-level networking interface ================================================ .. module:: socket :synopsis: Low-level networking interface. This module provides access to the BSD *socket* interface. It is available on all modern Unix systems, Windows, MacOS, and probably additional platforms. .. note:: Some behavior may be platform dependent, since calls are made to the operating system socket APIs. .. index:: object: socket The Python interface is a straightforward transliteration of the Unix system call and library interface for sockets to Python's object-oriented style: the :func:`.socket` function returns a :dfn:`socket object` whose methods implement the various socket system calls. Parameter types are somewhat higher-level than in the C interface: as with :meth:`read` and :meth:`write` operations on Python files, buffer allocation on receive operations is automatic, and buffer length is implicit on send operations. .. seealso:: Module :mod:`socketserver` Classes that simplify writing network servers. Module :mod:`ssl` A TLS/SSL wrapper for socket objects. Socket families --------------- Depending on the system and the build options, various socket families are supported by this module. The address format required by a particular socket object is automatically selected based on the address family specified when the socket object was created. Socket addresses are represented as follows: - The address of an :const:`AF_UNIX` socket bound to a file system node is represented as a string, using the file system encoding and the ``'surrogateescape'`` error handler (see :pep:`383`). An address in Linux's abstract namespace is returned as a :class:`bytes` object with an initial null byte; note that sockets in this namespace can communicate with normal file system sockets, so programs intended to run on Linux may need to deal with both types of address. A string or :class:`bytes` object can be used for either type of address when passing it as an argument. .. versionchanged:: 3.3 Previously, :const:`AF_UNIX` socket paths were assumed to use UTF-8 encoding. - A pair ``(host, port)`` is used for the :const:`AF_INET` address family, where *host* is a string representing either a hostname in Internet domain notation like ``'daring.cwi.nl'`` or an IPv4 address like ``'100.50.200.5'``, and *port* is an integer. - For :const:`AF_INET6` address family, a four-tuple ``(host, port, flowinfo, scopeid)`` is used, where *flowinfo* and *scopeid* represent the ``sin6_flowinfo`` and ``sin6_scope_id`` members in :const:`struct sockaddr_in6` in C. For :mod:`socket` module methods, *flowinfo* and *scopeid* can be omitted just for backward compatibility. Note, however, omission of *scopeid* can cause problems in manipulating scoped IPv6 addresses. - :const:`AF_NETLINK` sockets are represented as pairs ``(pid, groups)``. - Linux-only support for TIPC is available using the :const:`AF_TIPC` address family. TIPC is an open, non-IP based networked protocol designed for use in clustered computer environments. Addresses are represented by a tuple, and the fields depend on the address type. The general tuple form is ``(addr_type, v1, v2, v3 [, scope])``, where: - *addr_type* is one of :const:`TIPC_ADDR_NAMESEQ`, :const:`TIPC_ADDR_NAME`, or :const:`TIPC_ADDR_ID`. - *scope* is one of :const:`TIPC_ZONE_SCOPE`, :const:`TIPC_CLUSTER_SCOPE`, and :const:`TIPC_NODE_SCOPE`. - If *addr_type* is :const:`TIPC_ADDR_NAME`, then *v1* is the server type, *v2* is the port identifier, and *v3* should be 0. If *addr_type* is :const:`TIPC_ADDR_NAMESEQ`, then *v1* is the server type, *v2* is the lower port number, and *v3* is the upper port number. If *addr_type* is :const:`TIPC_ADDR_ID`, then *v1* is the node, *v2* is the reference, and *v3* should be set to 0. - A tuple ``(interface, )`` is used for the :const:`AF_CAN` address family, where *interface* is a string representing a network interface name like ``'can0'``. The network interface name ``''`` can be used to receive packets from all network interfaces of this family. - A string or a tuple ``(id, unit)`` is used for the :const:`SYSPROTO_CONTROL` protocol of the :const:`PF_SYSTEM` family. The string is the name of a kernel control using a dynamically-assigned ID. The tuple can be used if ID and unit number of the kernel control are known or if a registered ID is used. .. versionadded:: 3.3 - :const:`AF_BLUETOOTH` supports the following protocols and address formats: - :const:`BTPROTO_L2CAP` accepts ``(bdaddr, psm)`` where ``bdaddr`` is the Bluetooth address as a string and ``psm`` is an integer. - :const:`BTPROTO_RFCOMM` accepts ``(bdaddr, channel)`` where ``bdaddr`` is the Bluetooth address as a string and ``channel`` is an integer. - :const:`BTPROTO_HCI` accepts ``(device_id,)`` where ``device_id`` is either an integer or a string with the Bluetooth address of the interface. (This depends on your OS; NetBSD and DragonFlyBSD expect a Bluetooth address while everything else expects an integer.) .. versionchanged:: 3.2 NetBSD and DragonFlyBSD support added. - :const:`BTPROTO_SCO` accepts ``bdaddr`` where ``bdaddr`` is a :class:`bytes` object containing the Bluetooth address in a string format. (ex. ``b'12:23:34:45:56:67'``) This protocol is not supported under FreeBSD. - Certain other address families (:const:`AF_PACKET`, :const:`AF_CAN`) support specific representations. .. XXX document them! For IPv4 addresses, two special forms are accepted instead of a host address: the empty string represents :const:`INADDR_ANY`, and the string ``'<broadcast>'`` represents :const:`INADDR_BROADCAST`. This behavior is not compatible with IPv6, therefore, you may want to avoid these if you intend to support IPv6 with your Python programs. If you use a hostname in the *host* portion of IPv4/v6 socket address, the program may show a nondeterministic behavior, as Python uses the first address returned from the DNS resolution. The socket address will be resolved differently into an actual IPv4/v6 address, depending on the results from DNS resolution and/or the host configuration. For deterministic behavior use a numeric address in *host* portion. All errors raise exceptions. The normal exceptions for invalid argument types and out-of-memory conditions can be raised; starting from Python 3.3, errors related to socket or address semantics raise :exc:`OSError` or one of its subclasses (they used to raise :exc:`socket.error`). Non-blocking mode is supported through :meth:`~socket.setblocking`. A generalization of this based on timeouts is supported through :meth:`~socket.settimeout`. Module contents --------------- The module :mod:`socket` exports the following elements. Exceptions ^^^^^^^^^^ .. exception:: error A deprecated alias of :exc:`OSError`. .. versionchanged:: 3.3 Following :pep:`3151`, this class was made an alias of :exc:`OSError`. .. exception:: herror A subclass of :exc:`OSError`, this exception is raised for address-related errors, i.e. for functions that use *h_errno* in the POSIX C API, including :func:`gethostbyname_ex` and :func:`gethostbyaddr`. The accompanying value is a pair ``(h_errno, string)`` representing an error returned by a library call. *h_errno* is a numeric value, while *string* represents the description of *h_errno*, as returned by the :c:func:`hstrerror` C function. .. versionchanged:: 3.3 This class was made a subclass of :exc:`OSError`. .. exception:: gaierror A subclass of :exc:`OSError`, this exception is raised for address-related errors by :func:`getaddrinfo` and :func:`getnameinfo`. The accompanying value is a pair ``(error, string)`` representing an error returned by a library call. *string* represents the description of *error*, as returned by the :c:func:`gai_strerror` C function. The numeric *error* value will match one of the :const:`EAI_\*` constants defined in this module. .. versionchanged:: 3.3 This class was made a subclass of :exc:`OSError`. .. exception:: timeout A subclass of :exc:`OSError`, this exception is raised when a timeout occurs on a socket which has had timeouts enabled via a prior call to :meth:`~socket.settimeout` (or implicitly through :func:`~socket.setdefaulttimeout`). The accompanying value is a string whose value is currently always "timed out". .. versionchanged:: 3.3 This class was made a subclass of :exc:`OSError`. Constants ^^^^^^^^^ The AF_* and SOCK_* constants are now :class:`AddressFamily` and :class:`SocketKind` :class:`.IntEnum` collections. .. versionadded:: 3.4 .. data:: AF_UNIX AF_INET AF_INET6 These constants represent the address (and protocol) families, used for the first argument to :func:`.socket`. If the :const:`AF_UNIX` constant is not defined then this protocol is unsupported. More constants may be available depending on the system. .. data:: SOCK_STREAM SOCK_DGRAM SOCK_RAW SOCK_RDM SOCK_SEQPACKET These constants represent the socket types, used for the second argument to :func:`.socket`. More constants may be available depending on the system. (Only :const:`SOCK_STREAM` and :const:`SOCK_DGRAM` appear to be generally useful.) .. data:: SOCK_CLOEXEC SOCK_NONBLOCK These two constants, if defined, can be combined with the socket types and allow you to set some flags atomically (thus avoiding possible race conditions and the need for separate calls). .. seealso:: `Secure File Descriptor Handling <http://udrepper.livejournal.com/20407.html>`_ for a more thorough explanation. Availability: Linux >= 2.6.27. .. versionadded:: 3.2 .. data:: SO_* SOMAXCONN MSG_* SOL_* SCM_* IPPROTO_* IPPORT_* INADDR_* IP_* IPV6_* EAI_* AI_* NI_* TCP_* Many constants of these forms, documented in the Unix documentation on sockets and/or the IP protocol, are also defined in the socket module. They are generally used in arguments to the :meth:`setsockopt` and :meth:`getsockopt` methods of socket objects. In most cases, only those symbols that are defined in the Unix header files are defined; for a few symbols, default values are provided. .. data:: AF_CAN PF_CAN SOL_CAN_* CAN_* Many constants of these forms, documented in the Linux documentation, are also defined in the socket module. Availability: Linux >= 2.6.25. .. versionadded:: 3.3 .. data:: CAN_BCM CAN_BCM_* CAN_BCM, in the CAN protocol family, is the broadcast manager (BCM) protocol. Broadcast manager constants, documented in the Linux documentation, are also defined in the socket module. Availability: Linux >= 2.6.25. .. versionadded:: 3.4 .. data:: AF_RDS PF_RDS SOL_RDS RDS_* Many constants of these forms, documented in the Linux documentation, are also defined in the socket module. Availability: Linux >= 2.6.30. .. versionadded:: 3.3 .. data:: SIO_* RCVALL_* Constants for Windows' WSAIoctl(). The constants are used as arguments to the :meth:`~socket.socket.ioctl` method of socket objects. .. data:: TIPC_* TIPC related constants, matching the ones exported by the C socket API. See the TIPC documentation for more information. .. data:: AF_LINK Availability: BSD, OSX. .. versionadded:: 3.4 .. data:: has_ipv6 This constant contains a boolean value which indicates if IPv6 is supported on this platform. .. data:: BDADDR_ANY BDADDR_LOCAL These are string constants containing Bluetooth addresses with special meanings. For example, :const:`BDADDR_ANY` can be used to indicate any address when specifying the binding socket with :const:`BTPROTO_RFCOMM`. .. data:: HCI_FILTER HCI_TIME_STAMP HCI_DATA_DIR For use with :const:`BTPROTO_HCI`. :const:`HCI_FILTER` is not available for NetBSD or DragonFlyBSD. :const:`HCI_TIME_STAMP` and :const:`HCI_DATA_DIR` are not available for FreeBSD, NetBSD, or DragonFlyBSD. Functions ^^^^^^^^^ Creating sockets '''''''''''''''' The following functions all create :ref:`socket objects <socket-objects>`. .. function:: socket(family=AF_INET, type=SOCK_STREAM, proto=0, fileno=None) Create a new socket using the given address family, socket type and protocol number. The address family should be :const:`AF_INET` (the default), :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The socket type should be :const:`SOCK_STREAM` (the default), :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_`` constants. The protocol number is usually zero and may be omitted or in the case where the address family is :const:`AF_CAN` the protocol should be one of :const:`CAN_RAW` or :const:`CAN_BCM`. If *fileno* is specified, the other arguments are ignored, causing the socket with the specified file descriptor to return. Unlike :func:`socket.fromfd`, *fileno* will return the same socket and not a duplicate. This may help close a detached socket using :meth:`socket.close()`. The newly created socket is :ref:`non-inheritable <fd_inheritance>`. .. versionchanged:: 3.3 The AF_CAN family was added. The AF_RDS family was added. .. versionchanged:: 3.4 The CAN_BCM protocol was added. .. versionchanged:: 3.4 The returned socket is now non-inheritable. .. function:: socketpair([family[, type[, proto]]]) Build a pair of connected socket objects using the given address family, socket type, and protocol number. Address family, socket type, and protocol number are as for the :func:`.socket` function above. The default family is :const:`AF_UNIX` if defined on the platform; otherwise, the default is :const:`AF_INET`. Availability: Unix. The newly created sockets are :ref:`non-inheritable <fd_inheritance>`. .. versionchanged:: 3.2 The returned socket objects now support the whole socket API, rather than a subset. .. versionchanged:: 3.4 The returned sockets are now non-inheritable. .. function:: create_connection(address[, timeout[, source_address]]) Connect to a TCP service listening on the Internet *address* (a 2-tuple ``(host, port)``), and return the socket object. This is a higher-level function than :meth:`socket.connect`: if *host* is a non-numeric hostname, it will try to resolve it for both :data:`AF_INET` and :data:`AF_INET6`, and then try to connect to all possible addresses in turn until a connection succeeds. This makes it easy to write clients that are compatible to both IPv4 and IPv6. Passing the optional *timeout* parameter will set the timeout on the socket instance before attempting to connect. If no *timeout* is supplied, the global default timeout setting returned by :func:`getdefaulttimeout` is used. If supplied, *source_address* must be a 2-tuple ``(host, port)`` for the socket to bind to as its source address before connecting. If host or port are '' or 0 respectively the OS default behavior will be used. .. versionchanged:: 3.2 *source_address* was added. .. versionchanged:: 3.2 support for the :keyword:`with` statement was added. .. function:: fromfd(fd, family, type, proto=0) Duplicate the file descriptor *fd* (an integer as returned by a file object's :meth:`fileno` method) and build a socket object from the result. Address family, socket type and protocol number are as for the :func:`.socket` function above. The file descriptor should refer to a socket, but this is not checked --- subsequent operations on the object may fail if the file descriptor is invalid. This function is rarely needed, but can be used to get or set socket options on a socket passed to a program as standard input or output (such as a server started by the Unix inet daemon). The socket is assumed to be in blocking mode. The newly created socket is :ref:`non-inheritable <fd_inheritance>`. .. versionchanged:: 3.4 The returned socket is now non-inheritable. .. function:: fromshare(data) Instantiate a socket from data obtained from the :meth:`socket.share` method. The socket is assumed to be in blocking mode. Availability: Windows. .. versionadded:: 3.3 .. data:: SocketType This is a Python type object that represents the socket object type. It is the same as ``type(socket(...))``. Other functions ''''''''''''''' The :mod:`socket` module also offers various network-related services: .. function:: getaddrinfo(host, port, family=0, type=0, proto=0, flags=0) Translate the *host*/*port* argument into a sequence of 5-tuples that contain all the necessary arguments for creating a socket connected to that service. *host* is a domain name, a string representation of an IPv4/v6 address or ``None``. *port* is a string service name such as ``'http'``, a numeric port number or ``None``. By passing ``None`` as the value of *host* and *port*, you can pass ``NULL`` to the underlying C API. The *family*, *type* and *proto* arguments can be optionally specified in order to narrow the list of addresses returned. Passing zero as a value for each of these arguments selects the full range of results. The *flags* argument can be one or several of the ``AI_*`` constants, and will influence how results are computed and returned. For example, :const:`AI_NUMERICHOST` will disable domain name resolution and will raise an error if *host* is a domain name. The function returns a list of 5-tuples with the following structure: ``(family, type, proto, canonname, sockaddr)`` In these tuples, *family*, *type*, *proto* are all integers and are meant to be passed to the :func:`.socket` function. *canonname* will be a string representing the canonical name of the *host* if :const:`AI_CANONNAME` is part of the *flags* argument; else *canonname* will be empty. *sockaddr* is a tuple describing a socket address, whose format depends on the returned *family* (a ``(address, port)`` 2-tuple for :const:`AF_INET`, a ``(address, port, flow info, scope id)`` 4-tuple for :const:`AF_INET6`), and is meant to be passed to the :meth:`socket.connect` method. The following example fetches address information for a hypothetical TCP connection to ``example.org`` on port 80 (results may differ on your system if IPv6 isn't enabled):: >>> socket.getaddrinfo("example.org", 80, proto=socket.IPPROTO_TCP) [(<AddressFamily.AF_INET6: 10>, <SocketType.SOCK_STREAM: 1>, 6, '', ('2606:2800:220:1:248:1893:25c8:1946', 80, 0, 0)), (<AddressFamily.AF_INET: 2>, <SocketType.SOCK_STREAM: 1>, 6, '', ('93.184.216.34', 80))] .. versionchanged:: 3.2 parameters can now be passed using keyword arguments. .. function:: getfqdn([name]) Return a fully qualified domain name for *name*. If *name* is omitted or empty, it is interpreted as the local host. To find the fully qualified name, the hostname returned by :func:`gethostbyaddr` is checked, followed by aliases for the host, if available. The first name which includes a period is selected. In case no fully qualified domain name is available, the hostname as returned by :func:`gethostname` is returned. .. function:: gethostbyname(hostname) Translate a host name to IPv4 address format. The IPv4 address is returned as a string, such as ``'100.50.200.5'``. If the host name is an IPv4 address itself it is returned unchanged. See :func:`gethostbyname_ex` for a more complete interface. :func:`gethostbyname` does not support IPv6 name resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. .. function:: gethostbyname_ex(hostname) Translate a host name to IPv4 address format, extended interface. Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary host name responding to the given *ip_address*, *aliaslist* is a (possibly empty) list of alternative host names for the same address, and *ipaddrlist* is a list of IPv4 addresses for the same interface on the same host (often but not always a single address). :func:`gethostbyname_ex` does not support IPv6 name resolution, and :func:`getaddrinfo` should be used instead for IPv4/v6 dual stack support. .. function:: gethostname() Return a string containing the hostname of the machine where the Python interpreter is currently executing. If you want to know the current machine's IP address, you may want to use ``gethostbyname(gethostname())``. This operation assumes that there is a valid address-to-host mapping for the host, and the assumption does not always hold. Note: :func:`gethostname` doesn't always return the fully qualified domain name; use :func:`getfqdn` for that. .. function:: gethostbyaddr(ip_address) Return a triple ``(hostname, aliaslist, ipaddrlist)`` where *hostname* is the primary host name responding to the given *ip_address*, *aliaslist* is a (possibly empty) list of alternative host names for the same address, and *ipaddrlist* is a list of IPv4/v6 addresses for the same interface on the same host (most likely containing only a single address). To find the fully qualified domain name, use the function :func:`getfqdn`. :func:`gethostbyaddr` supports both IPv4 and IPv6. .. function:: getnameinfo(sockaddr, flags) Translate a socket address *sockaddr* into a 2-tuple ``(host, port)``. Depending on the settings of *flags*, the result can contain a fully-qualified domain name or numeric address representation in *host*. Similarly, *port* can contain a string port name or a numeric port number. .. function:: getprotobyname(protocolname) Translate an Internet protocol name (for example, ``'icmp'``) to a constant suitable for passing as the (optional) third argument to the :func:`.socket` function. This is usually only needed for sockets opened in "raw" mode (:const:`SOCK_RAW`); for the normal socket modes, the correct protocol is chosen automatically if the protocol is omitted or zero. .. function:: getservbyname(servicename[, protocolname]) Translate an Internet service name and protocol name to a port number for that service. The optional protocol name, if given, should be ``'tcp'`` or ``'udp'``, otherwise any protocol will match. .. function:: getservbyport(port[, protocolname]) Translate an Internet port number and protocol name to a service name for that service. The optional protocol name, if given, should be ``'tcp'`` or ``'udp'``, otherwise any protocol will match. .. function:: ntohl(x) Convert 32-bit positive integers from network to host byte order. On machines where the host byte order is the same as network byte order, this is a no-op; otherwise, it performs a 4-byte swap operation. .. function:: ntohs(x) Convert 16-bit positive integers from network to host byte order. On machines where the host byte order is the same as network byte order, this is a no-op; otherwise, it performs a 2-byte swap operation. .. function:: htonl(x) Convert 32-bit positive integers from host to network byte order. On machines where the host byte order is the same as network byte order, this is a no-op; otherwise, it performs a 4-byte swap operation. .. function:: htons(x) Convert 16-bit positive integers from host to network byte order. On machines where the host byte order is the same as network byte order, this is a no-op; otherwise, it performs a 2-byte swap operation. .. function:: inet_aton(ip_string) Convert an IPv4 address from dotted-quad string format (for example, '123.45.67.89') to 32-bit packed binary format, as a bytes object four characters in length. This is useful when conversing with a program that uses the standard C library and needs objects of type :c:type:`struct in_addr`, which is the C type for the 32-bit packed binary this function returns. :func:`inet_aton` also accepts strings with less than three dots; see the Unix manual page :manpage:`inet(3)` for details. If the IPv4 address string passed to this function is invalid, :exc:`OSError` will be raised. Note that exactly what is valid depends on the underlying C implementation of :c:func:`inet_aton`. :func:`inet_aton` does not support IPv6, and :func:`inet_pton` should be used instead for IPv4/v6 dual stack support. .. function:: inet_ntoa(packed_ip) Convert a 32-bit packed IPv4 address (a bytes object four characters in length) to its standard dotted-quad string representation (for example, '123.45.67.89'). This is useful when conversing with a program that uses the standard C library and needs objects of type :c:type:`struct in_addr`, which is the C type for the 32-bit packed binary data this function takes as an argument. If the byte sequence passed to this function is not exactly 4 bytes in length, :exc:`OSError` will be raised. :func:`inet_ntoa` does not support IPv6, and :func:`inet_ntop` should be used instead for IPv4/v6 dual stack support. .. function:: inet_pton(address_family, ip_string) Convert an IP address from its family-specific string format to a packed, binary format. :func:`inet_pton` is useful when a library or network protocol calls for an object of type :c:type:`struct in_addr` (similar to :func:`inet_aton`) or :c:type:`struct in6_addr`. Supported values for *address_family* are currently :const:`AF_INET` and :const:`AF_INET6`. If the IP address string *ip_string* is invalid, :exc:`OSError` will be raised. Note that exactly what is valid depends on both the value of *address_family* and the underlying implementation of :c:func:`inet_pton`. Availability: Unix (maybe not all platforms), Windows. .. versionchanged:: 3.4 Windows support added .. function:: inet_ntop(address_family, packed_ip) Convert a packed IP address (a bytes object of some number of characters) to its standard, family-specific string representation (for example, ``'7.10.0.5'`` or ``'5aef:2b::8'``). :func:`inet_ntop` is useful when a library or network protocol returns an object of type :c:type:`struct in_addr` (similar to :func:`inet_ntoa`) or :c:type:`struct in6_addr`. Supported values for *address_family* are currently :const:`AF_INET` and :const:`AF_INET6`. If the string *packed_ip* is not the correct length for the specified address family, :exc:`ValueError` will be raised. :exc:`OSError` is raised for errors from the call to :func:`inet_ntop`. Availability: Unix (maybe not all platforms), Windows. .. versionchanged:: 3.4 Windows support added .. XXX: Are sendmsg(), recvmsg() and CMSG_*() available on any non-Unix platforms? The old (obsolete?) 4.2BSD form of the interface, in which struct msghdr has no msg_control or msg_controllen members, is not currently supported. .. function:: CMSG_LEN(length) Return the total length, without trailing padding, of an ancillary data item with associated data of the given *length*. This value can often be used as the buffer size for :meth:`~socket.recvmsg` to receive a single item of ancillary data, but :rfc:`3542` requires portable applications to use :func:`CMSG_SPACE` and thus include space for padding, even when the item will be the last in the buffer. Raises :exc:`OverflowError` if *length* is outside the permissible range of values. Availability: most Unix platforms, possibly others. .. versionadded:: 3.3 .. function:: CMSG_SPACE(length) Return the buffer size needed for :meth:`~socket.recvmsg` to receive an ancillary data item with associated data of the given *length*, along with any trailing padding. The buffer space needed to receive multiple items is the sum of the :func:`CMSG_SPACE` values for their associated data lengths. Raises :exc:`OverflowError` if *length* is outside the permissible range of values. Note that some systems might support ancillary data without providing this function. Also note that setting the buffer size using the results of this function may not precisely limit the amount of ancillary data that can be received, since additional data may be able to fit into the padding area. Availability: most Unix platforms, possibly others. .. versionadded:: 3.3 .. function:: getdefaulttimeout() Return the default timeout in seconds (float) for new socket objects. A value of ``None`` indicates that new socket objects have no timeout. When the socket module is first imported, the default is ``None``. .. function:: setdefaulttimeout(timeout) Set the default timeout in seconds (float) for new socket objects. When the socket module is first imported, the default is ``None``. See :meth:`~socket.settimeout` for possible values and their respective meanings. .. function:: sethostname(name) Set the machine's hostname to *name*. This will raise an :exc:`OSError` if you don't have enough rights. Availability: Unix. .. versionadded:: 3.3 .. function:: if_nameindex() Return a list of network interface information (index int, name string) tuples. :exc:`OSError` if the system call fails. Availability: Unix. .. versionadded:: 3.3 .. function:: if_nametoindex(if_name) Return a network interface index number corresponding to an interface name. :exc:`OSError` if no interface with the given name exists. Availability: Unix. .. versionadded:: 3.3 .. function:: if_indextoname(if_index) Return a network interface name corresponding to an interface index number. :exc:`OSError` if no interface with the given index exists. Availability: Unix. .. versionadded:: 3.3 .. _socket-objects: Socket Objects -------------- Socket objects have the following methods. Except for :meth:`~socket.makefile`, these correspond to Unix system calls applicable to sockets. .. method:: socket.accept() Accept a connection. The socket must be bound to an address and listening for connections. The return value is a pair ``(conn, address)`` where *conn* is a *new* socket object usable to send and receive data on the connection, and *address* is the address bound to the socket on the other end of the connection. The newly created socket is :ref:`non-inheritable <fd_inheritance>`. .. versionchanged:: 3.4 The socket is now non-inheritable. .. method:: socket.bind(address) Bind the socket to *address*. The socket must not already be bound. (The format of *address* depends on the address family --- see above.) .. method:: socket.close() Mark the socket closed. The underlying system resource (e.g. a file descriptor) is also closed when all file objects from :meth:`makefile()` are closed. Once that happens, all future operations on the socket object will fail. The remote end will receive no more data (after queued data is flushed). Sockets are automatically closed when they are garbage-collected, but it is recommended to :meth:`close` them explicitly, or to use a :keyword:`with` statement around them. .. note:: :meth:`close()` releases the resource associated with a connection but does not necessarily close the connection immediately. If you want to close the connection in a timely fashion, call :meth:`shutdown()` before :meth:`close()`. .. method:: socket.connect(address) Connect to a remote socket at *address*. (The format of *address* depends on the address family --- see above.) .. method:: socket.connect_ex(address) Like ``connect(address)``, but return an error indicator instead of raising an exception for errors returned by the C-level :c:func:`connect` call (other problems, such as "host not found," can still raise exceptions). The error indicator is ``0`` if the operation succeeded, otherwise the value of the :c:data:`errno` variable. This is useful to support, for example, asynchronous connects. .. method:: socket.detach() Put the socket object into closed state without actually closing the underlying file descriptor. The file descriptor is returned, and can be reused for other purposes. .. versionadded:: 3.2 .. method:: socket.dup() Duplicate the socket. The newly created socket is :ref:`non-inheritable <fd_inheritance>`. .. versionchanged:: 3.4 The socket is now non-inheritable. .. method:: socket.fileno() Return the socket's file descriptor (a small integer). This is useful with :func:`select.select`. Under Windows the small integer returned by this method cannot be used where a file descriptor can be used (such as :func:`os.fdopen`). Unix does not have this limitation. .. method:: socket.get_inheritable() Get the :ref:`inheritable flag <fd_inheritance>` of the socket's file descriptor or socket's handle: ``True`` if the socket can be inherited in child processes, ``False`` if it cannot. .. versionadded:: 3.4 .. method:: socket.getpeername() Return the remote address to which the socket is connected. This is useful to find out the port number of a remote IPv4/v6 socket, for instance. (The format of the address returned depends on the address family --- see above.) On some systems this function is not supported. .. method:: socket.getsockname() Return the socket's own address. This is useful to find out the port number of an IPv4/v6 socket, for instance. (The format of the address returned depends on the address family --- see above.) .. method:: socket.getsockopt(level, optname[, buflen]) Return the value of the given socket option (see the Unix man page :manpage:`getsockopt(2)`). The needed symbolic constants (:const:`SO_\*` etc.) are defined in this module. If *buflen* is absent, an integer option is assumed and its integer value is returned by the function. If *buflen* is present, it specifies the maximum length of the buffer used to receive the option in, and this buffer is returned as a bytes object. It is up to the caller to decode the contents of the buffer (see the optional built-in module :mod:`struct` for a way to decode C structures encoded as byte strings). .. method:: socket.gettimeout() Return the timeout in seconds (float) associated with socket operations, or ``None`` if no timeout is set. This reflects the last call to :meth:`setblocking` or :meth:`settimeout`. .. method:: socket.ioctl(control, option) :platform: Windows The :meth:`ioctl` method is a limited interface to the WSAIoctl system interface. Please refer to the `Win32 documentation <http://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx>`_ for more information. On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl` functions may be used; they accept a socket object as their first argument.


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