mirror of
https://github.com/python/cpython.git
synced 2024-11-26 19:34:19 +08:00
55 lines
2.4 KiB
TeX
55 lines
2.4 KiB
TeX
\section{\module{select} ---
|
|
Waiting for I/O completion}
|
|
|
|
\declaremodule{builtin}{select}
|
|
\modulesynopsis{Wait for I/O completion on multiple streams.}
|
|
|
|
|
|
This module provides access to the function \cfunction{select()}
|
|
available in most operating systems. Note that on Windows, it only
|
|
works for sockets; on other operating systems, it also works for other
|
|
file types (in particular, on \UNIX{}, it works on pipes). It cannot
|
|
be used on regular files to determine whether a file has grown since
|
|
it was last read.
|
|
|
|
The module defines the following:
|
|
|
|
\begin{excdesc}{error}
|
|
The exception raised when an error occurs. The accompanying value is
|
|
a pair containing the numeric error code from \cdata{errno} and the
|
|
corresponding string, as would be printed by the \C{} function
|
|
\cfunction{perror()}.
|
|
\end{excdesc}
|
|
|
|
\begin{funcdesc}{select}{iwtd, owtd, ewtd\optional{, timeout}}
|
|
This is a straightforward interface to the \UNIX{} \cfunction{select()}
|
|
system call. The first three arguments are lists of `waitable
|
|
objects': either integers representing \UNIX{} file descriptors or
|
|
objects with a parameterless method named \method{fileno()} returning
|
|
such an integer. The three lists of waitable objects are for input,
|
|
output and `exceptional conditions', respectively. Empty lists are
|
|
allowed. The optional \var{timeout} argument specifies a time-out as a
|
|
floating point number in seconds. When the \var{timeout} argument
|
|
is omitted the function blocks until at least one file descriptor is
|
|
ready. A time-out value of zero specifies a poll and never blocks.
|
|
|
|
The return value is a triple of lists of objects that are ready:
|
|
subsets of the first three arguments. When the time-out is reached
|
|
without a file descriptor becoming ready, three empty lists are
|
|
returned.
|
|
|
|
Amongst the acceptable object types in the lists are Python file
|
|
objects (e.g. \code{sys.stdin}, or objects returned by
|
|
\function{open()} or \function{os.popen()}), socket objects
|
|
returned by \function{socket.socket()},%
|
|
\withsubitem{(in module socket)}{\ttindex{socket()}}
|
|
\withsubitem{(in module os)}{\ttindex{popen()}}
|
|
and the module \module{stdwin}\refbimodindex{stdwin} which happens to
|
|
define a function
|
|
\function{fileno()}\withsubitem{(in module stdwin)}{\ttindex{fileno()}}
|
|
for just this purpose. You may
|
|
also define a \dfn{wrapper} class yourself, as long as it has an
|
|
appropriate \method{fileno()} method (that really returns a \UNIX{}
|
|
file descriptor, not just a random integer).
|
|
\end{funcdesc}
|