socket — Low-level networking interface¶Source code: Lib/socket.py
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.
The Python interface is a straightforward transliteration of the Unix system
call and library interface for sockets to Python’s object-oriented style: the
socket() function returns a socket object whose methods implement
the various socket system calls. Parameter types are somewhat higher-level than
in the C interface: as with read() and write() operations on Python
files, buffer allocation on receive operations is automatic, and buffer length
is implicit on send operations.
See also
socketserversslDepending 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 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 bytes-like 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
bytes-like object can be used for either type of address when
passing it as an argument.
Changed in version 3.3: Previously,
AF_UNIXsocket paths were assumed to use UTF-8 encoding.Changed in version 3.5: Writable bytes-like object is now accepted.
A pair (host, port) is used for the 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 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 struct sockaddr_in6 in C. For
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.
AF_NETLINK sockets are represented as pairs (pid, groups).
Linux-only support for TIPC is available using the 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 TIPC_ADDR_NAMESEQ, TIPC_ADDR_NAME,
or TIPC_ADDR_ID.
scope is one of TIPC_ZONE_SCOPE, TIPC_CLUSTER_SCOPE, and
TIPC_NODE_SCOPE.
If addr_type is TIPC_ADDR_NAME, then v1 is the server type, v2 is
the port identifier, and v3 should be 0.
If addr_type is 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 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 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 SYSPROTO_CONTROL
protocol of the 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.
New in version 3.3.
AF_BLUETOOTH supports the following protocols and address
formats:
BTPROTO_L2CAP accepts (bdaddr, psm) where bdaddr is
the Bluetooth address as a string and psm is an integer.
BTPROTO_RFCOMM accepts (bdaddr, channel) where bdaddr
is the Bluetooth address as a string and channel is an integer.
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.)
Changed in version 3.2: NetBSD and DragonFlyBSD support added.
BTPROTO_SCO accepts bdaddr where bdaddr is a
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.
AF_ALG is a Linux-only socket based interface to Kernel
cryptography. An algorithm socket is configured with a tuple of two to four
elements (type, name [, feat [, mask]]), where:
aead, hash,
skcipher or rng.sha256, hmac(sha256), cbc(aes) or drbg_nopr_ctr_aes256.Availability Linux 2.6.38, some algorithm types require more recent Kernels.
New in version 3.6.
Certain other address families (AF_PACKET, AF_CAN)
support specific representations.
For IPv4 addresses, two special forms are accepted instead of a host address:
the empty string represents INADDR_ANY, and the string
'<broadcast>' represents 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 OSError or one of its
subclasses (they used to raise socket.error).
Non-blocking mode is supported through setblocking(). A
generalization of this based on timeouts is supported through
settimeout().
The module socket exports the following elements.
socket.herror¶A subclass of OSError, this exception is raised for
address-related errors, i.e. for functions that use h_errno in the POSIX
C API, including gethostbyname_ex() and 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
hstrerror() C function.
Changed in version 3.3: This class was made a subclass of OSError.
socket.gaierror¶A subclass of OSError, this exception is raised for
address-related errors by getaddrinfo() and 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 gai_strerror() C function. The
numeric error value will match one of the EAI_* constants
defined in this module.
Changed in version 3.3: This class was made a subclass of OSError.
socket.timeout¶A subclass of OSError, this exception is raised when a timeout
occurs on a socket which has had timeouts enabled via a prior call to
settimeout() (or implicitly through
setdefaulttimeout()). The accompanying value is a string
whose value is currently always “timed out”.
Changed in version 3.3: This class was made a subclass of OSError.
The AF_* and SOCK_* constants are now
AddressFamilyandSocketKindIntEnumcollections.New in version 3.4.
socket.AF_UNIX¶socket.AF_INET¶socket.AF_INET6¶These constants represent the address (and protocol) families, used for the
first argument to socket(). If the AF_UNIX constant is not
defined then this protocol is unsupported. More constants may be available
depending on the system.
socket.SOCK_STREAM¶socket.SOCK_DGRAM¶socket.SOCK_RAW¶socket.SOCK_RDM¶socket.SOCK_SEQPACKET¶These constants represent the socket types, used for the second argument to
socket(). More constants may be available depending on the system.
(Only SOCK_STREAM and SOCK_DGRAM appear to be generally
useful.)
socket.SOCK_CLOEXEC¶socket.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).
See also
Secure File Descriptor Handling for a more thorough explanation.
Availability: Linux >= 2.6.27.
New in version 3.2.
SO_*socket.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 setsockopt() and 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.
Changed in version 3.6: SO_DOMAIN, SO_PROTOCOL, SO_PEERSEC, SO_PASSSEC,
TCP_USER_TIMEOUT, TCP_CONGESTION were added.
socket.AF_CAN¶socket.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.
New in version 3.3.
socket.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.
New in version 3.4.
socket.CAN_RAW_FD_FRAMES¶Enables CAN FD support in a CAN_RAW socket. This is disabled by default. This allows your application to send both CAN and CAN FD frames; however, you one must accept both CAN and CAN FD frames when reading from the socket.
This constant is documented in the Linux documentation.
Availability: Linux >= 3.6.
New in version 3.5.
socket.AF_RDS¶socket.PF_RDS¶socket.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.
New in version 3.3.
socket.SIO_RCVALL¶socket.SIO_KEEPALIVE_VALS¶socket.SIO_LOOPBACK_FAST_PATH¶RCVALL_*Constants for Windows’ WSAIoctl(). The constants are used as arguments to the
ioctl() method of socket objects.
Changed in version 3.6: SIO_LOOPBACK_FAST_PATH was added.
TIPC_*TIPC related constants, matching the ones exported by the C socket API. See the TIPC documentation for more information.
socket.AF_ALG¶socket.SOL_ALG¶ALG_*Constants for Linux Kernel cryptography.
Availability: Linux >= 2.6.38.
New in version 3.6.
socket.AF_LINK¶Availability: BSD, OSX.
New in version 3.4.
socket.has_ipv6¶This constant contains a boolean value which indicates if IPv6 is supported on this platform.
socket.BDADDR_ANY¶socket.BDADDR_LOCAL¶These are string constants containing Bluetooth addresses with special
meanings. For example, BDADDR_ANY can be used to indicate
any address when specifying the binding socket with
BTPROTO_RFCOMM.
socket.HCI_FILTER¶socket.HCI_TIME_STAMP¶socket.HCI_DATA_DIR¶For use with BTPROTO_HCI. HCI_FILTER is not
available for NetBSD or DragonFlyBSD. HCI_TIME_STAMP and
HCI_DATA_DIR are not available for FreeBSD, NetBSD, or
DragonFlyBSD.
The following functions all create socket objects.
socket.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 AF_INET (the default),
AF_INET6, AF_UNIX, AF_CAN or AF_RDS. The
socket type should be SOCK_STREAM (the default),
SOCK_DGRAM, 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 AF_CAN the protocol should be one
of CAN_RAW or CAN_BCM. If fileno is specified, the other
arguments are ignored, causing the socket with the specified file descriptor
to return. Unlike socket.fromfd(), fileno will return the same
socket and not a duplicate. This may help close a detached socket using
socket.close().
The newly created socket is non-inheritable.
Changed in version 3.3: The AF_CAN family was added. The AF_RDS family was added.
Changed in version 3.4: The CAN_BCM protocol was added.
Changed in version 3.4: The returned socket is now non-inheritable.
socket.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 socket() function above. The default family is AF_UNIX
if defined on the platform; otherwise, the default is AF_INET.
The newly created sockets are non-inheritable.
Changed in version 3.2: The returned socket objects now support the whole socket API, rather than a subset.
Changed in version 3.4: The returned sockets are now non-inheritable.
Changed in version 3.5: Windows support added.
socket.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 socket.connect(): if host is a non-numeric hostname,
it will try to resolve it for both AF_INET and 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
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.
Changed in version 3.2: source_address was added.
socket.fromfd(fd, family, type, proto=0)¶Duplicate the file descriptor fd (an integer as returned by a file object’s
fileno() method) and build a socket object from the result. Address
family, socket type and protocol number are as for the 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 non-inheritable.
Changed in version 3.4: The returned socket is now non-inheritable.
Instantiate a socket from data obtained from the socket.share()
method. The socket is assumed to be in blocking mode.
Availability: Windows.
New in version 3.3.
socket.SocketType¶This is a Python type object that represents the socket object type. It is the
same as type(socket(...)).
The socket module also offers various network-related services:
socket.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, 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 socket() function. canonname will be
a string representing the canonical name of the host if
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
AF_INET, a (address, port, flow info, scope id) 4-tuple for
AF_INET6), and is meant to be passed to the 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))]
Changed in version 3.2: parameters can now be passed using keyword arguments.
socket.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 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
gethostname() is returned.
socket.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 gethostbyname_ex() for a more complete
interface. gethostbyname() does not support IPv6 name resolution, and
getaddrinfo() should be used instead for IPv4/v6 dual stack support.
socket.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). gethostbyname_ex() does not support IPv6 name
resolution, and getaddrinfo() should be used instead for IPv4/v6 dual
stack support.
socket.gethostname()¶Return a string containing the hostname of the machine where the Python interpreter is currently executing.
Note: gethostname() doesn’t always return the fully qualified domain
name; use getfqdn() for that.
socket.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 getfqdn(). gethostbyaddr() supports
both IPv4 and IPv6.
socket.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.
socket.getprotobyname(protocolname)¶Translate an Internet protocol name (for example, 'icmp') to a constant
suitable for passing as the (optional) third argument to the socket()
function. This is usually only needed for sockets opened in “raw” mode
(SOCK_RAW); for the normal socket modes, the correct protocol is chosen
automatically if the protocol is omitted or zero.
socket.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.
socket.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.
socket.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.
socket.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.
socket.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.
socket.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.
socket.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 struct in_addr, which is the C type
for the 32-bit packed binary this function returns.
inet_aton() also accepts strings with less than three dots; see the
Unix manual page inet(3) for details.
If the IPv4 address string passed to this function is invalid,
OSError will be raised. Note that exactly what is valid depends on
the underlying C implementation of inet_aton().
inet_aton() does not support IPv6, and inet_pton() should be used
instead for IPv4/v6 dual stack support.
socket.inet_ntoa(packed_ip)¶Convert a 32-bit packed IPv4 address (a bytes-like object four
bytes 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 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, OSError will be raised. inet_ntoa() does not
support IPv6, and inet_ntop() should be used instead for IPv4/v6 dual
stack support.
Changed in version 3.5: Writable bytes-like object is now accepted.
socket.inet_pton(address_family, ip_string)¶Convert an IP address from its family-specific string format to a packed,
binary format. inet_pton() is useful when a library or network protocol
calls for an object of type struct in_addr (similar to
inet_aton()) or struct in6_addr.
Supported values for address_family are currently AF_INET and
AF_INET6. If the IP address string ip_string is invalid,
OSError will be raised. Note that exactly what is valid depends on
both the value of address_family and the underlying implementation of
inet_pton().
Availability: Unix (maybe not all platforms), Windows.
Changed in version 3.4: Windows support added
socket.inet_ntop(address_family, packed_ip)¶Convert a packed IP address (a bytes-like object of some number of
bytes) to its standard, family-specific string representation (for
example, '7.10.0.5' or '5aef:2b::8').
inet_ntop() is useful when a library or network protocol returns an
object of type struct in_addr (similar to inet_ntoa()) or
struct in6_addr.
Supported values for address_family are currently AF_INET and
AF_INET6. If the bytes object packed_ip is not the correct
length for the specified address family, ValueError will be raised.
OSError is raised for errors from the call to inet_ntop().
Availability: Unix (maybe not all platforms), Windows.
Changed in version 3.4: Windows support added
Changed in version 3.5: Writable bytes-like object is now accepted.
socket.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 recvmsg() to
receive a single item of ancillary data, but RFC 3542 requires
portable applications to use CMSG_SPACE() and thus include
space for padding, even when the item will be the last in the
buffer. Raises OverflowError if length is outside the
permissible range of values.
Availability: most Unix platforms, possibly others.
New in version 3.3.
socket.CMSG_SPACE(length)¶Return the buffer size needed for 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 CMSG_SPACE()
values for their associated data lengths. Raises
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.
New in version 3.3.
socket.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.
socket.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
settimeout() for possible values and their respective
meanings.
socket.sethostname(name)¶Set the machine’s hostname to name. This will raise an
OSError if you don’t have enough rights.
Availability: Unix.
New in version 3.3.
socket.if_nameindex()¶Return a list of network interface information
(index int, name string) tuples.
OSError if the system call fails.
Availability: Unix.
New in version 3.3.
Socket objects have the following methods. Except for
makefile(), these correspond to Unix system calls applicable
to sockets.
Changed in version 3.2: Support for the context manager protocol was added. Exiting the
context manager is equivalent to calling close().
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 non-inheritable.
Changed in version 3.4: The socket is now non-inheritable.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
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.)
socket.close()¶Mark the socket closed. The underlying system resource (e.g. a file
descriptor) is also closed when all file objects from 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 close() them explicitly, or to use a
with statement around them.
Changed in version 3.6: OSError is now raised if an error occurs when the underlying
close() call is made.
Note
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 shutdown()
before close().
socket.connect(address)¶Connect to a remote socket at address. (The format of address depends on the address family — see above.)
If the connection is interrupted by a signal, the method waits until the
connection completes, or raise a socket.timeout on timeout, if the
signal handler doesn’t raise an exception and the socket is blocking or has
a timeout. For non-blocking sockets, the method raises an
InterruptedError exception if the connection is interrupted by a
signal (or the exception raised by the signal handler).
Changed in version 3.5: The method now waits until the connection completes instead of raising an
InterruptedError exception if the connection is interrupted by a
signal, the signal handler doesn’t raise an exception and the socket is
blocking or has a timeout (see the PEP 475 for the rationale).
socket.connect_ex(address)¶Like connect(address), but return an error indicator instead of raising an
exception for errors returned by the C-level 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
errno variable. This is useful to support, for example, asynchronous
connects.
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.
New in version 3.2.
socket.dup()¶Duplicate the socket.
The newly created socket is non-inheritable.
Changed in version 3.4: The socket is now non-inheritable.
socket.fileno()¶Return the socket’s file descriptor (a small integer), or -1 on failure. This
is useful with select.select().
Under Windows the small integer returned by this method cannot be used where a
file descriptor can be used (such as os.fdopen()). Unix does not have
this limitation.
socket.get_inheritable()¶Get the inheritable flag of the socket’s file
descriptor or socket’s handle: True if the socket can be inherited in
child processes, False if it cannot.
New in version 3.4.
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.
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.)
socket.getsockopt(level, optname[, buflen])¶Return the value of the given socket option (see the Unix man page
getsockopt(2)). The needed symbolic constants (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 struct for a way
to decode C structures encoded as byte strings).
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
setblocking() or settimeout().
socket.ioctl(control, option)¶| Platform: | Windows |
|---|
The ioctl() method is a limited interface to the WSAIoctl system
interface. Please refer to the Win32 documentation for more
information.
On other platforms, the generic fcntl.fcntl() and fcntl.ioctl()
functions may be used; they accept a socket object as their first argument.
Currently only the following control codes are supported:
SIO_RCVALL, SIO_KEEPALIVE_VALS, and SIO_LOOPBACK_FAST_PATH.
Changed in version 3.6: SIO_LOOPBACK_FAST_PATH was added.
socket.listen([backlog])¶Enable a server to accept connections. If backlog is specified, it must be at least 0 (if it is lower, it is set to 0); it specifies the number of unaccepted connections that the system will allow before refusing new connections. If not specified, a default reasonable value is chosen.
Changed in version 3.5: The backlog parameter is now optional.
socket.makefile(mode='r', buffering=None, *, encoding=None, errors=None, newline=None)¶Return a file object associated with the socket. The exact returned
type depends on the arguments given to makefile(). These arguments are
interpreted the same way as by the built-in open() function, except
the only supported mode values are 'r' (default), 'w' and 'b'.
The socket must be in blocking mode; it can have a timeout, but the file object’s internal buffer may end up in an inconsistent state if a timeout occurs.
Closing the file object returned by makefile() won’t close the
original socket unless all other file objects have been closed and
socket.close() has been called on the socket object.
Note
On Windows, the file-like object created by makefile() cannot be
used where a file object with a file descriptor is expected, such as the
stream arguments of subprocess.Popen().
socket.recv(bufsize[, flags])¶Receive data from the socket. The return value is a bytes object representing the data received. The maximum amount of data to be received at once is specified by bufsize. See the Unix manual page recv(2) for the meaning of the optional argument flags; it defaults to zero.
Note
For best match with hardware and network realities, the value of bufsize should be a relatively small power of 2, for example, 4096.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
socket.recvfrom(bufsize[, flags])¶Receive data from the socket. The return value is a pair (bytes, address)
where bytes is a bytes object representing the data received and address is the
address of the socket sending the data. See the Unix manual page
recv(2) for the meaning of the optional argument flags; it defaults
to zero. (The format of address depends on the address family — see above.)
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
socket.recvmsg(bufsize[, ancbufsize[, flags]])¶Receive normal data (up to bufsize bytes) and ancillary data from
the socket. The ancbufsize argument sets the size in bytes of
the internal buffer used to receive the ancillary data; it defaults
to 0, meaning that no ancillary data will be received. Appropriate
buffer sizes for ancillary data can be calculated using
CMSG_SPACE() or CMSG_LEN(), and items which do not fit
into the buffer might be truncated or discarded. The flags
argument defaults to 0 and has the same meaning as for
recv().
The return value is a 4-tuple: (data, ancdata, msg_flags,
address). The data item is a bytes object holding the
non-ancillary data received. The ancdata item is a list of zero
or more tuples (cmsg_level, cmsg_type, cmsg_data) representing
the ancillary data (control messages) received: cmsg_level and
cmsg_type are integers specifying the protocol level and
protocol-specific type respectively, and cmsg_data is a
bytes object holding the associated data. The msg_flags
item is the bitwise OR of various flags indicating conditions on
the received message; see your system documentation for details.
If the receiving socket is unconnected, address is the address of
the sending socket, if available; otherwise, its value is
unspecified.
On some systems, sendmsg() and recvmsg() can be used to
pass file descriptors between processes over an AF_UNIX
socket. When this facility is used (it is often restricted to
SOCK_STREAM sockets), recvmsg() will return, in its
ancillary data, items of the form (socket.SOL_SOCKET,
socket.SCM_RIGHTS, fds), where fds is a bytes object
representing the new file descriptors as a binary array of the
native C int type. If recvmsg() raises an
exception after the system call returns, it will first attempt to
close any file descriptors received via this mechanism.
Some systems do not indicate the truncated length of ancillary data
items which have been only partially received. If an item appears
to extend beyond the end of the buffer, recvmsg() will issue
a RuntimeWarning, and will return the part of it which is
inside the buffer provided it has not been truncated before the
start of its associated data.
On systems which support the SCM_RIGHTS mechanism, the
following function will receive up to maxfds file descriptors,
returning the message data and a list containing the descriptors
(while ignoring unexpected conditions such as unrelated control
messages being received). See also sendmsg().
import socket, array
def recv_fds(sock, msglen, maxfds):
fds = array.array("i") # Array of ints
msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
for cmsg_level, cmsg_type, cmsg_data in ancdata:
if (cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS):
# Append data, ignoring any truncated integers at the end.
fds.fromstring(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
return msg, list(fds)
Availability: most Unix platforms, possibly others.
New in version 3.3.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
socket.recvmsg_into(buffers[, ancbufsize[, flags]])¶Receive normal data and ancillary data from the socket, behaving as
recvmsg() would, but scatter the non-ancillary data into a
series of buffers instead of returning a new bytes object. The
buffers argument must be an iterable of objects that export
writable buffers (e.g. bytearray objects); these will be
filled with successive chunks of the non-ancillary data until it
has all been written or there are no more buffers. The operating
system may set a limit (sysconf() value SC_IOV_MAX)
on the number of buffers that can be used. The ancbufsize and
flags arguments have the same meaning as for recvmsg().
The return value is a 4-tuple: (nbytes, ancdata, msg_flags,
address), where nbytes is the total number of bytes of
non-ancillary data written into the buffers, and ancdata,
msg_flags and address are the same as for recvmsg().
Example:
>>> import socket
>>> s1, s2 = socket.socketpair()
>>> b1 = bytearray(b'----')
>>> b2 = bytearray(b'0123456789')
>>> b3 = bytearray(b'--------------')
>>> s1.send(b'Mary had a little lamb')
22
>>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3])
(22, [], 0, None)
>>> [b1, b2, b3]
[bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')]
Availability: most Unix platforms, possibly others.
New in version 3.3.
socket.recvfrom_into(buffer[, nbytes[, flags]])¶Receive data from the socket, writing it into buffer instead of creating a
new bytestring. The return value is a pair (nbytes, address) where nbytes is
the number of bytes received and address is the address of the socket sending
the data. See the Unix manual page recv(2) for the meaning of the
optional argument flags; it defaults to zero. (The format of address
depends on the address family — see above.)
socket.recv_into(buffer[, nbytes[, flags]])¶Receive up to nbytes bytes from the socket, storing the data into a buffer rather than creating a new bytestring. If nbytes is not specified (or 0), receive up to the size available in the given buffer. Returns the number of bytes received. See the Unix manual page recv(2) for the meaning of the optional argument flags; it defaults to zero.
socket.send(bytes[, flags])¶Send data to the socket. The socket must be connected to a remote socket. The
optional flags argument has the same meaning as for recv() above.
Returns the number of bytes sent. Applications are responsible for checking that
all data has been sent; if only some of the data was transmitted, the
application needs to attempt delivery of the remaining data. For further
information on this topic, consult the Socket Programming HOWTO.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
socket.sendall(bytes[, flags])¶Send data to the socket. The socket must be connected to a remote socket. The
optional flags argument has the same meaning as for recv() above.
Unlike send(), this method continues to send data from bytes until
either all data has been sent or an error occurs. None is returned on
success. On error, an exception is raised, and there is no way to determine how
much data, if any, was successfully sent.
Changed in version 3.5: The socket timeout is no more reset each time data is sent successfully. The socket timeout is now the maximum total duration to send all data.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
socket.sendto(bytes, address)¶socket.sendto(bytes, flags, address)Send data to the socket. The socket should not be connected to a remote socket,
since the destination socket is specified by address. The optional flags
argument has the same meaning as for recv() above. Return the number of
bytes sent. (The format of address depends on the address family — see
above.)
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
socket.sendmsg(buffers[, ancdata[, flags[, address]]])¶Send normal and ancillary data to the socket, gathering the
non-ancillary data from a series of buffers and concatenating it
into a single message. The buffers argument specifies the
non-ancillary data as an iterable of
bytes-like objects
(e.g. bytes objects); the operating system may set a limit
(sysconf() value SC_IOV_MAX) on the number of buffers
that can be used. The ancdata argument specifies the ancillary
data (control messages) as an iterable of zero or more tuples
(cmsg_level, cmsg_type, cmsg_data), where cmsg_level and
cmsg_type are integers specifying the protocol level and
protocol-specific type respectively, and cmsg_data is a
bytes-like object holding the associated data. Note that
some systems (in particular, systems without CMSG_SPACE())
might support sending only one control message per call. The
flags argument defaults to 0 and has the same meaning as for
send(). If address is supplied and not None, it sets a
destination address for the message. The return value is the
number of bytes of non-ancillary data sent.
The following function sends the list of file descriptors fds
over an AF_UNIX socket, on systems which support the
SCM_RIGHTS mechanism. See also recvmsg().
import socket, array
def send_fds(sock, msg, fds):
return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])
Availability: most Unix platforms, possibly others.
New in version 3.3.
Changed in version 3.5: If the system call is interrupted and the signal handler does not raise
an exception, the method now retries the system call instead of raising
an InterruptedError exception (see PEP 475 for the rationale).
socket.sendmsg_afalg([msg, ]*, op[, iv[, assoclen[, flags]]])¶Specialized version of sendmsg() for AF_ALG socket.
Set mode, IV, AEAD associated data length and flags for AF_ALG socket.
Availability: Linux >= 2.6.38
New in version 3.6.
socket.sendfile(file, offset=0, count=None)¶Send a file until EOF is reached by using high-performance
os.sendfile and return the total number of bytes which were sent.
file must be a regular file object opened in binary mode. If
os.sendfile is not available (e.g. Windows) or file is not a
regular file send() will be used instead. offset tells from where to
start reading the file. If specified, count is the total number of bytes
to transmit as opposed to sending the file until EOF is reached. File
position is updated on return or also in case of error in which case
file.tell() can be used to figure out the number of
bytes which were sent. The socket must be of SOCK_STREAM type.
Non-blocking sockets are not supported.
New in version 3.5.
socket.set_inheritable(inheritable)¶Set the inheritable flag of the socket’s file descriptor or socket’s handle.
New in version 3.4.
socket.setblocking(flag)¶Set blocking or non-blocking mode of the socket: if flag is false, the socket is set to non-blocking, else to blocking mode.
This method is a shorthand for certain settimeout() calls:
sock.setblocking(True) is equivalent to sock.settimeout(None)sock.setblocking(False) is equivalent to sock.settimeout(0.0)socket.settimeout(value)¶Set a timeout on blocking socket operations. The value argument can be a
nonnegative floating point number expressing seconds, or None.
If a non-zero value is given, subsequent socket operations will raise a
timeout exception if the timeout period value has elapsed before
the operation has completed. If zero is given, the socket is put in
non-blocking mode. If None is given, the socket is put in blocking mode.
For further information, please consult the notes on socket timeouts.
socket.setsockopt(level, optname, value: int)¶socket.setsockopt(level, optname, value: buffer)socket.setsockopt(level, optname, None, optlen: int)Set the value of the given socket option (see the Unix manual page
setsockopt(2)). The needed symbolic constants are defined in the
socket module (SO_* etc.). The value can be an integer,
None or a bytes-like object representing a buffer. In the later
case it is up to the caller to ensure that the bytestring contains the
proper bits (see the optional built-in module struct for a way to
encode C structures as bytestrings). When value is set to None,
optlen argument is required. It’s equivalent to call setsockopt C
function with optval=NULL and optlen=optlen.
Changed in version 3.5: Writable bytes-like object is now accepted.
Changed in version 3.6: setsockopt(level, optname, None, optlen: int) form added.
socket.shutdown(how)¶Shut down one or both halves of the connection. If how is SHUT_RD,
further receives are disallowed. If how is SHUT_WR, further sends
are disallowed. If how is SHUT_RDWR, further sends and receives are
disallowed.
Duplicate a socket and prepare it for sharing with a target process. The
target process must be provided with process_id. The resulting bytes object
can then be passed to the target process using some form of interprocess
communication and the socket can be recreated there using fromshare().
Once this method has been called, it is safe to close the socket since
the operating system has already duplicated it for the target process.
Availability: Windows.
New in version 3.3.
Note that there are no methods read() or write(); use
recv() and send() without flags argument instead.
Socket objects also have these (read-only) attributes that correspond to the
values given to the socket constructor.
socket.family¶The socket family.
socket.type¶The socket type.
socket.proto¶The socket protocol.
A socket object can be in one of three modes: blocking, non-blocking, or
timeout. Sockets are by default always created in blocking mode, but this
can be changed by calling setdefaulttimeout().
select can be used to know when and whether a socket is available for
reading or writing.timeout exception)
or if the system returns an error.Note
At the operating system level, sockets in timeout mode are internally set
in non-blocking mode. Also, the blocking and timeout modes are shared between
file descriptors and socket objects that refer to the same network endpoint.
This implementation detail can have visible consequences if e.g. you decide
to use the fileno() of a socket.
connect method¶The connect() operation is also subject to the timeout
setting, and in general it is recommended to call settimeout()
before calling connect() or pass a timeout parameter to
create_connection(). However, the system network stack may also
return a connection timeout error of its own regardless of any Python socket
timeout setting.
accept method¶If getdefaulttimeout() is not None, sockets returned by
the accept() method inherit that timeout. Otherwise, the
behaviour depends on settings of the listening socket:
accept() is in blocking mode;accept() is in blocking or non-blocking mode
is operating system-dependent. If you want to ensure cross-platform
behaviour, it is recommended you manually override this setting.Here are four minimal example programs using the TCP/IP protocol: a server that
echoes all data that it receives back (servicing only one client), and a client
using it. Note that a server must perform the sequence socket(),
bind(), listen(), accept() (possibly
repeating the accept() to service more than one client), while a
client only needs the sequence socket(), connect(). Also
note that the server does not sendall()/recv() on
the socket it is listening on but on the new socket returned by
accept().
The first two examples support IPv4 only.
# Echo server program
import socket
HOST = '' # Symbolic name meaning all available interfaces
PORT = 50007 # Arbitrary non-privileged port
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
s.bind((HOST, PORT))
s.listen(1)
conn, addr = s.accept()
with conn:
print('Connected by', addr)
while True:
data = conn.recv(1024)
if not data: break
conn.sendall(data)
# Echo client program
import socket
HOST = 'daring.cwi.nl' # The remote host
PORT = 50007 # The same port as used by the server
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
s.connect((HOST, PORT))
s.sendall(b'Hello, world')
data = s.recv(1024)
print('Received', repr(data))
The next two examples are identical to the above two, but support both IPv4 and IPv6. The server side will listen to the first address family available (it should listen to both instead). On most of IPv6-ready systems, IPv6 will take precedence and the server may not accept IPv4 traffic. The client side will try to connect to the all addresses returned as a result of the name resolution, and sends traffic to the first one connected successfully.
# Echo server program
import socket
import sys
HOST = None # Symbolic name meaning all available interfaces
PORT = 50007 # Arbitrary non-privileged port
s = None
for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC,
socket.SOCK_STREAM, 0, socket.AI_PASSIVE):
af, socktype, proto, canonname, sa = res
try:
s = socket.socket(af, socktype, proto)
except OSError as msg:
s = None
continue
try:
s.bind(sa)
s.listen(1)
except OSError as msg:
s.close()
s = None
continue
break
if s is None:
print('could not open socket')
sys.exit(1)
conn, addr = s.accept()
with conn:
print('Connected by', addr)
while True:
data = conn.recv(1024)
if not data: break
conn.send(data)
# Echo client program
import socket
import sys
HOST = 'daring.cwi.nl' # The remote host
PORT = 50007 # The same port as used by the server
s = None
for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
af, socktype, proto, canonname, sa = res
try:
s = socket.socket(af, socktype, proto)
except OSError as msg:
s = None
continue
try:
s.connect(sa)
except OSError as msg:
s.close()
s = None
continue
break
if s is None:
print('could not open socket')
sys.exit(1)
with s:
s.sendall(b'Hello, world')
data = s.recv(1024)
print('Received', repr(data))
The next example shows how to write a very simple network sniffer with raw sockets on Windows. The example requires administrator privileges to modify the interface:
import socket
# the public network interface
HOST = socket.gethostbyname(socket.gethostname())
# create a raw socket and bind it to the public interface
s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP)
s.bind((HOST, 0))
# Include IP headers
s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
# receive all packages
s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
# receive a package
print(s.recvfrom(65565))
# disabled promiscuous mode
s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)
The last example shows how to use the socket interface to communicate to a CAN network using the raw socket protocol. To use CAN with the broadcast manager protocol instead, open a socket with:
socket.socket(socket.AF_CAN, socket.SOCK_DGRAM, socket.CAN_BCM)
After binding (CAN_RAW) or connecting (CAN_BCM) the socket, you
can use the socket.send(), and the socket.recv() operations (and
their counterparts) on the socket object as usual.
This example might require special privileges:
import socket
import struct
# CAN frame packing/unpacking (see 'struct can_frame' in <linux/can.h>)
can_frame_fmt = "=IB3x8s"
can_frame_size = struct.calcsize(can_frame_fmt)
def build_can_frame(can_id, data):
can_dlc = len(data)
data = data.ljust(8, b'\x00')
return struct.pack(can_frame_fmt, can_id, can_dlc, data)
def dissect_can_frame(frame):
can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame)
return (can_id, can_dlc, data[:can_dlc])
# create a raw socket and bind it to the 'vcan0' interface
s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
s.bind(('vcan0',))
while True:
cf, addr = s.recvfrom(can_frame_size)
print('Received: can_id=%x, can_dlc=%x, data=%s' % dissect_can_frame(cf))
try:
s.send(cf)
except OSError:
print('Error sending CAN frame')
try:
s.send(build_can_frame(0x01, b'\x01\x02\x03'))
except OSError:
print('Error sending CAN frame')
Running an example several times with too small delay between executions, could lead to this error:
OSError: [Errno 98] Address already in use
This is because the previous execution has left the socket in a TIME_WAIT
state, and can’t be immediately reused.
There is a socket flag to set, in order to prevent this,
socket.SO_REUSEADDR:
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((HOST, PORT))
the SO_REUSEADDR flag tells the kernel to reuse a local socket in
TIME_WAIT state, without waiting for its natural timeout to expire.
See also
For an introduction to socket programming (in C), see the following papers:
both in the UNIX Programmer’s Manual, Supplementary Documents 1 (sections PS1:7 and PS1:8). The platform-specific reference material for the various socket-related system calls are also a valuable source of information on the details of socket semantics. For Unix, refer to the manual pages; for Windows, see the WinSock (or Winsock 2) specification. For IPv6-ready APIs, readers may want to refer to RFC 3493 titled Basic Socket Interface Extensions for IPv6.