19.1. 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.

備註

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.

也參考

Module socketserver
Classes that simplify writing network servers.
Module ssl
A TLS/SSL wrapper for socket objects.

19.1.1. 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 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.

    3.3 版更變: Previously, AF_UNIX socket paths were assumed to use UTF-8 encoding.

    3.5 版更變: 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 IPv4 addresses, two special forms are accepted instead of a host address: '' represents INADDR_ANY, which is used to bind to all interfaces, 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.

  • 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.

    3.7 版更變: For multicast addresses (with scopeid meaningful) address may not contain %scope (or zone id) part. This information is superfluous and may be safely omitted (recommended).

  • 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.

    • CAN_ISOTP protocol require a tuple (interface, rx_addr, tx_addr) where both additional parameters are unsigned long integer that represent a CAN identifier (standard or extended).

  • 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.

    3.3 版新加入.

  • 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.)

      3.2 版更變: 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:

    • type is the algorithm type as string, e.g. aead, hash, skcipher or rng.
    • name is the algorithm name and operation mode as string, e.g. sha256, hmac(sha256), cbc(aes) or drbg_nopr_ctr_aes256.
    • feat and mask are unsigned 32bit integers.

    Availability Linux 2.6.38, some algorithm types require more recent Kernels.

    3.6 版新加入.

  • AF_VSOCK allows communication between virtual machines and their hosts. The sockets are represented as a (CID, port) tuple where the context ID or CID and port are integers.

    Availability: Linux >= 4.8 QEMU >= 2.8 ESX >= 4.0 ESX Workstation >= 6.5

    3.7 版新加入.

  • Certain other address families (AF_PACKET, AF_CAN) support specific representations.

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().

19.1.2. Module contents

The module socket exports the following elements.

19.1.2.1. Exceptions

exception socket.error

A deprecated alias of OSError.

3.3 版更變: Following PEP 3151, this class was made an alias of OSError.

exception 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.

3.3 版更變: This class was made a subclass of OSError.

exception 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.

3.3 版更變: This class was made a subclass of OSError.

exception 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」.

3.3 版更變: This class was made a subclass of OSError.

19.1.2.2. Constants

The AF_* and SOCK_* constants are now AddressFamily and SocketKind IntEnum collections.

3.4 版新加入.

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).

也參考

Secure File Descriptor Handling for a more thorough explanation.

Availability: Linux >= 2.6.27.

3.2 版新加入.

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.

3.6 版更變: SO_DOMAIN, SO_PROTOCOL, SO_PEERSEC, SO_PASSSEC, TCP_USER_TIMEOUT, TCP_CONGESTION were added.

3.6.5 版更變: On Windows, TCP_FASTOPEN, TCP_KEEPCNT appear if run-time Windows supports.

3.7 版更變: TCP_NOTSENT_LOWAT was added.

On Windows, TCP_KEEPIDLE, TCP_KEEPINTVL appear if run-time Windows supports.

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.

3.3 版新加入.

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.

3.4 版新加入.

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.

3.5 版新加入.

socket.CAN_ISOTP

CAN_ISOTP, in the CAN protocol family, is the ISO-TP (ISO 15765-2) protocol. ISO-TP constants, documented in the Linux documentation.

Availability: Linux >= 2.6.25

3.7 版新加入.

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.

3.3 版新加入.

socket.