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Python Library Reference |  |
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Python Library Reference | |
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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 the setblocking() method.
The module socket exports the following constants and functions:
(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.
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.
(error, string)
representing an error returned by a library call.
string represents the description of error, as returned
by the gai_strerror() C function.
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 Lib/httplib.py and other library files
for a typical usage of the function.
New in version 2.2.
'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.
(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.
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).
(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.
(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.
'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.
'tcp' or
'udp'.
Warning: This does not do any certificate verification!
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.
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 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.
type(socket(...)).
See Also:
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Python Library Reference | |
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