This module provides access to the BSD socket interface.
It is available on all modern Unix systems, Windows, MacOS, BeOS,
OS/2, and probably additional platforms.
For an introduction to socket programming (in C), see the following
papers: An Introductory 4.3BSD Interprocess Communication
Tutorial, by Stuart Sechrest and An Advanced 4.3BSD
Interprocess Communication Tutorial, by Samuel J. Leffler et al,
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 2553 titled
Basic Socket Interface Extensions for IPv6.
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.
Socket addresses are represented as follows:
A single string is used for the AF_UNIX address family.
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 integral port number.
For AF_INET6 address family, a four-tuple
(host, port, flowinfo, scopeid) is
used, where flowinfo and scopeid represents
sin6_flowinfo and sin6_scope_id member 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. Other address families are currently not supported.
The address format required by a particular socket object is
automatically selected based on the address family specified when the
socket object was created.
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.
The behavior is not available for IPv6 for backward compatibility,
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; errors
related to socket or address semantics raise the error
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 constants and functions:
exceptionerror
This exception is raised for socket-related errors.
The accompanying value is either a string telling what went wrong or a
pair (errno, string)
representing an error returned by a system
call, similar to the value accompanying os.error.
See the module errno, which contains
names for the error codes defined by the underlying operating system.
exceptionherror
This exception is raised for address-related errors, i.e. for
functions that use h_errno in the C API, including
gethostbyname_ex() and gethostbyaddr().
The accompanying value is a pair (h_errno, string)
representing an error returned by a library call. string
represents the description of h_errno, as returned by
the hstrerror() C function.
exceptiongaierror
This exception is raised for address-related errors, for
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 error value will match one of the EAI_* constants
defined in this module.
exceptiontimeout
This exception is raised when a timeout occurs on a socket which has
had timeouts enabled via a prior call to settimeout(). The
accompanying value is a string whose value is currently always ``timed
out''.
New in version 2.3.
AF_UNIX
AF_INET
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.
SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
SOCK_RDM
SOCK_SEQPACKET
These constants represent the socket types,
used for the second argument to socket().
(Only SOCK_STREAM and
SOCK_DGRAM appear to be generally useful.)
SO_*
SOMAXCONN
MSG_*
SOL_*
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.
has_ipv6
This constant contains a boolean value which indicates if IPv6 is
supported on this platform.
New in version 2.3.
Resolves the host/port argument, into a sequence of
5-tuples that contain all the necessary argument for the sockets
manipulation. host is a domain name, a string representation of
IPv4/v6 address or None.
port is a string service name (like 'http'), a numeric
port number or None.
The rest of the arguments are optional and must be numeric if
specified. For host and port, by passing either an empty
string or None, you can pass NULL to the C API. The
getaddrinfo() function returns a list of 5-tuples with
the following structure:
(family, socktype, proto, canonname,
sockaddr)
family, socktype, proto are all integer and are meant to
be passed to the socket() function.
canonname is a string representing the canonical name of the host.
It can be a numeric IPv4/v6 address when AI_CANONNAME is specified
for a numeric host.
sockaddr is a tuple describing a socket address, as described above.
See the source for the httplib and other library modules
for a typical usage of the function.
New in version 2.2.
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, then 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 is
returned.
New in version 2.0.
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.
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.
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: gethostname() doesn't always return the fully qualified
domain name; use gethostbyaddr(gethostname())
(see below).
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.
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.
New in version 2.2.
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.
getservbyname(
servicename, protocolname)
Translate an Internet service name and protocol name to a port number
for that service. The protocol name should be 'tcp' or
'udp'.
socket(
family, type[, proto])
Create a new socket using the given address family, socket type and
protocol number. The address family should be AF_INET, AF_INET6 or
AF_UNIX. The socket type should be SOCK_STREAM,
SOCK_DGRAM or perhaps one of the other "SOCK_" constants.
The protocol number is usually zero and may be omitted in that case.
ssl(
sock[, keyfile, certfile])
Initiate a SSL connection over the socket sock. keyfile is
the name of a PEM formatted file that contains your private
key. certfile is a PEM formatted certificate chain file. On
success, a new SSLObject is returned.
Warning:
This does not do any certificate verification!
fromfd(
fd, family, type[, proto])
Build a socket object from an existing file descriptor (an integer as
returned by a file object's fileno() method). 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.
Availability: Unix.
ntohl(
x)
Convert 32-bit 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.
ntohs(
x)
Convert 16-bit 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.
htonl(
x)
Convert 32-bit 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.
htons(
x)
Convert 16-bit 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.
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 string 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.
If the IPv4 address string passed to this function is invalid,
socket.error 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
getnameinfo() should be used instead for IPv4/v6 dual stack
support.
inet_ntoa(
packed_ip)
Convert a 32-bit packed IPv4 address (a string 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
struct in_addr, which is the C type for the 32-bit packed
binary data this function takes as an argument.
If the string passed to this function is not exactly 4 bytes in
length, socket.error will be raised.
inet_ntoa() does not support IPv6, and
getnameinfo() should be used instead for IPv4/v6 dual stack
support.
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,
socket.error 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).
New in version 2.3.
inet_ntop(
address_family, packed_ip)
Convert a packed IP address (a string of some number of characters) 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 string packed_ip is not the correct length for the
specified address family, ValueError will be raised. A
socket.error is raised for errors from the call to
inet_ntop().
Availability: Unix (maybe not all platforms).
New in version 2.3.
getdefaulttimeout(
)
Return the default timeout in floating seconds 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.
New in version 2.3.
setdefaulttimeout(
timeout)
Set the default timeout in floating seconds 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.
New in version 2.3.
SocketType
This is a Python type object that represents the socket object type.
It is the same as type(socket(...)).
