\section{Standard Module \sectcode{posixfile}}

\bimodindex{posixfile}

\indexii{posix}{file object}

This module implements some additional functionality over the built-in

file objects. In particular, it implements file locking, control over

the file flags, and an easy interface to duplicate the file object.

The module defines a new file object, the posixfile object. It

inherits all the standard file object methods and adds the methods

described below.

To instantiate a posixfile object, use the \code{open()} function in

the posixfile module. The resulting object looks and feels the same as

a standard file object.

The posixfile module defines the following constants:

\renewcommand{\indexsubitem}{(in module posixfile)}

\begin{datadesc}{SEEK_SET}

offset is calculated from the start of the file

\end{datadesc}

\begin{datadesc}{SEEK_CUR}

offset is calculated from the current position in the file

\end{datadesc}

\begin{datadesc}{SEEK_END}

offset is calculated from the end of the file

\end{datadesc}

The posixfile module defines the following functions:

\renewcommand{\indexsubitem}{(in module posixfile)}

\begin{funcdesc}{open}{filename\, mode}

Create a new posixfile object with the given filename and mode. The

filename and mode are interpreted the same way as the \code{open()}

builtin function.

\end{funcdesc}

\begin{funcdesc}{openfile}{fileobject}

Create a new posixfile object with the given standard file object.

The resulting object has the same filename and mode as the original

file object.

\end{funcdesc}

The posixfile object defines the following additional methods:

\renewcommand{\indexsubitem}{(posixfile method)}

\begin{funcdesc}{lock}{fmt\, len\, start\, whence}

Lock the specified section of the file that the file object is

referring to. The arguments \code{\var{len}}, \code{\var{start}}

and \code{\var{whence}} are optional with the understanding that

if \code{\var{start}} is used \code{\var{len}} becomes mandatory,

and if \code{\var{whence}} is used \code{\var{len}} and

\code{\var{start}} become mandatory. The format is explained

below in a table. The length argument specifies the length of the

section that should be locked. The default is \code{0}. The start

specifies the starting offset of the section. The default is

\code{0}. The whence argument specifies where the offset is

relative to. It accepts one of the constants \code{SEEK_SET},

\code{SEEK_CUR} or \code{SEEK_END}. The default is \code{SEEK_SET}.

For more information about the arguments refer to the fcntl

manual page on your system.

\end{funcdesc}

\begin{funcdesc}{flags}{fmt}

Set the specified flags for the file that the file object is referring

to. The new flags are ORed with the old flags, unless specified

otherwise. The format is explained below in a table. Without

arguments a string indicating the current flags is returned (this is

the same as the '?'modifier). For more information about the flags

refer to the fcntl manual page on your system.

\end{funcdesc}

\begin{funcdesc}{dup}{}

Duplicate the file object and the underlying file pointer and file

descriptor. The resulting object behaves as if it were newly

opened.

\end{funcdesc}

\begin{funcdesc}{dup2}{fd}

Duplicate the file object and the underlying file pointer and file

descriptor. The new object will have the given file descriptor.

Otherwise the resulting object behaves as if it were newly opened.

\end{funcdesc}

\begin{funcdesc}{file}{}

Return the standard file object that the posixfile object is based

on. This is sometimes necessary for functions that insist on a

standard file object.

\end{funcdesc}

All methods return \code{IOError} when the request fails.

Format characters for the \code{lock()} method have the following meaning:

\begin{tableii}{|c|l|}{samp}{Format}{Meaning}

\lineii{u}{unlock the specified region}

\lineii{r}{request a read lock for the specified section}

\lineii{w}{request a write lock for the specified section}

\end{tableii}

In addition the following modifiers can be added to the format:

\begin{tableiii}{|c|l|c|}{samp}{Modifier}{Meaning}{Notes}

\lineiii{|}{wait until the lock has been granted}{}

\lineiii{?}{return the first lock conflicting with the requested lock,

or \code{None} if there is no conflict.}{(1)}

\end{tableiii}

Note:

(1) The lock returned is in the format \code{(mode, len, start,

whence, pid)} where mode is a character representing the type of lock

('r' or 'w'). This modifier prevents a request from being granted; it

is for query purposes only.

Format character for the \code{flags()} method have the following meaning:

\begin{tableii}{|c|l|}{samp}{Format}{Meaning}

\lineii{a}{append only flag}

\lineii{c}{close on exec flag}

\lineii{n}{no delay flag (also called non-blocking flag)}

\lineii{s}{synchronization flag}

\end{tableii}

In addition the following modifiers can be added to the format:

\begin{tableiii}{|c|l|c|}{samp}{Modifier}{Meaning}{Notes}

\lineiii{!}{turn the specified flags 'off', instead of the default 'on'}{(1)}

\lineiii{=}{replace the flags, instead of the default 'OR' operation}{(1)}

\lineiii{?}{return a string in which the characters represent the flags that

are set.}{(2)}

\end{tableiii}

Note:

(1) The \code{!} and \code{=} modifiers are mutually exclusive.

(2) This string represents the flag after they may have been altered

by the same call.

Examples:

\bcode\begin{verbatim}

\end{verbatim}\ecode

\section{Built-in module \sectcode{fcntl}}

\bimodindex{fcntl}

\indexii{UNIX}{file control}

\indexii{UNIX}{IO control}

This module performs file control and IO control on file descriptors.

It is an interface to the \dfn{fcntl()} and \dfn{ioctl()} \UNIX routines.

File descriptors can be obtained with the \dfn{fileno()} method of a

file or socket object.

The module defines the following functions:

\renewcommand{\indexsubitem}{(in module struct)}

\begin{funcdesc}{fcntl}{fd\, op\, arg}

Perform the requested operation on file descriptor \code{\var{fd}}.

The operation is defined by \code{\var{op}} and is operating system

dependent. Typically these codes can be retrieved from the library

module \code{FCNTL}. The argument \code{\var{arg}} is optional. When

it is missing it is interpreted as the integer value \code{0}. When

it is present, it can either be an integer value, or a string. With

the argument missing or an integer value, the return value of this

function is the integer return value of the real \code{fcntl()}

call. When the argument is a string it represents a binary

structure, e.g. created by \code{struct.pack()}. The binary data is

copied to a buffer whose address is passed to the real \code{fcntl()}

call. The return value after a successful call is the contents of

the buffer, converted to a string object. In the case the

\code{fcntl()} fails, an \code{IOError} will be raised.

\end{funcdesc}

\begin{funcdesc}{ioctl}{fd\, op\, arg}

This function is identical to the \code{fcntl()} function, except

that the operations are typically defined in the library module

\code{IOCTL}.

\end{funcdesc}

If the library modules \code{FCNTL} or \code{IOCTL} are missing, you

can find the opcodes in the C include files \code{sys/fcntl} and

\code{sys/ioctl}. You can create the modules yourself with the h2py

script, found in the \code{Demo/scripts} directory.

Examples (all on a SVR4 compliant system):

\bcode\begin{verbatim}

\end{verbatim}\ecode

Note that in the first example the return value variable \code{rv} will

hold an integer value; in the second example it will hold a string

value.