\section{Built-in Module \sectcode{MacOS}}
\bimodindex{MacOS}

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

This module provides access to MacOS specific functionality in the
python interpreter, such as how the interpreter eventloop functions
and the like. Use with care.

Note the capitalisation of the module name, this is a historical
artefact.

\begin{excdesc}{Error}
This exception is raised on MacOS generated errors, either from
functions in this module or from other mac-specific modules like the
toolbox interfaces. The arguments are the integer error code (the
\var{OSErr} value) and a textual description of the error code.
Symbolic names for all known error codes are defined in the standard
module \var{macerrors}.
\end{excdesc}

\begin{funcdesc}{SetHighLevelEventHandler}{handler}
Pass a python function that will be called upon reception of a
high-level event. The previous handler is returned. The handler
function is called with the event as argument.

Note that your event handler is currently only called dependably if
your main event loop is in \var{stdwin}.
\end{funcdesc}

\begin{funcdesc}{AcceptHighLevelEvent}{}
Read a high-level event. The return value is a tuple \code{(sender,
refcon, data)}.
\end{funcdesc}

\begin{funcdesc}{SetScheduleTimes}{fgi\, fgy \optional{\, bgi\, bgy}}
Controls how often the interpreter checks the event queue and how
long it will yield the processor to other processes. \var{fgi}
specifies after how many clicks (one click is one 60th of a second)
the interpreter should check the event queue, and \var{fgy} specifies
for how many clicks the CPU should be yielded when in the
foreground. The optional \var{bgi} and \var{bgy} allow you to specify
different values to use when python runs in the background, otherwise
the background values will be set the the same as the foreground
values. The function returns nothing.

The default values, which are based on minimal empirical testing, are 12, 1, 6
and 2 respectively.
\end{funcdesc}

\begin{funcdesc}{EnableAppswitch}{onoff}
Enable or disable the python event loop, based on the value of
\var{onoff}. The old value is returned. If the event loop is disabled
no time is granted to other applications, checking for command-period
is not performed and it is impossible to switch applications. This
should only be used by programs providing their own complete event
loop.

Note that based on the compiler used to build python it is still
possible to loose events even with the python event loop disabled. If
you have a \code{sys.stdout} window its handler will often also look
in the event queue. Making sure nothing is ever printed works around
this.
\end{funcdesc}

\begin{funcdesc}{HandleEvent}{ev}
Pass the event record \code{ev} back to the python event loop, or
possibly to the handler for the \code{sys.stdout} window (based on the
compiler used to build python). This allows python programs that do
their own event handling to still have some command-period and
window-switching capability.
\end{funcdesc}

\begin{funcdesc}{GetErrorString}{errno}
Return the textual description of MacOS error code \var{errno}.
\end{funcdesc}

\begin{funcdesc}{splash}{resid}
This function will put a splash window
on-screen, with the contents of the DLOG resource specified by
\code{resid}. Calling with a zero argument will remove the splash
screen. This function is useful if you want an applet to post a splash screen
early in initialization without first having to load numerous
extension modules.
\end{funcdesc}

\begin{funcdesc}{DebugStr}{message \optional{\, object}}
Drop to the low-level debugger with message \var{message}. The
optional \var{object} argument is not used, but can easily be
inspected from the debugger.

Note that you should use this function with extreme care: if no
low-level debugger like MacsBug is installed this call will crash your
system. It is intended mainly for developers of Python extension
modules.
\end{funcdesc}

\begin{funcdesc}{openrf}{name \optional{\, mode}}
Open the resource fork of a file. Arguments are the same as for the
builtin function \code{open}. The object returned has file-like
semantics, but it is not a python file object, so there may be subtle
differences.
\end{funcdesc}