This module provides access to the BSD socket interface.
It is available on Unix systems that support this interface.
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 Unix manual pages for the various socket-related
system calls are also a valuable source of information on the details of
socket semantics.
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 a single string for the
AF_UNIX address family and as a pair
(host, port) 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 IP address like '100.50.200.5',
and port is an integral port number. 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 IP addresses, two special forms are accepted instead of a host
address: the empty string represents INADDR_ANY, and the string
'<broadcast>' represents INADDR_BROADCAST.
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 the
setblocking() method.
The module socket exports the following constants and functions:
This exception is raised for socket- or address-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.
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.
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.
Translate a host name to IP address format. The IP address is
returned as a string, e.g., '100.50.200.5'. If the host name
is an IP address itself it is returned unchanged. See
gethostbyname_ex() for a more complete interface.
Translate a host name to IP 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 IP addresses for the same interface on the same
host (often but not always a single address).
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, use gethostbyname(gethostname()).
Note: gethostname() doesn't always return the fully qualified
domain name; use gethostbyaddr(gethostname())(see below).
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 IP addresses for the same interface
on the same host (most likely containing only a single address).
To find the fully qualified domain name, check hostname and the
items of aliaslist for an entry containing at least one period.
Translate an Internet protocol name (e.g. '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.
Create a new socket using the given address family, socket type and
protocol number. The address family should be AF_INET 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.
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 (e.g. a server started by the Unix inet
daemon).
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.
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.
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.
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.
