mirror of https://github.com/python/cpython
Update the example in "Calling Python Functions from C" to use
METH_VARARGS conventions and PyArg_ParseTuple(), and document the flag and where to look for PyArg_ParseTuple() info. Response to comment from Don Bashford <bashford@scripps.edu>.
This commit is contained in:
Fred Drake
parent
c46973c89b
commit
5e8aa549d1
141
Doc/ext/ext.tex
141
Doc/ext/ext.tex
|
|
@ -72,8 +72,8 @@ The compilation of an extension module depends on its intended use as
|
|||
well as on your system setup; details are given in a later section.
|
||||
|
||||
|
||||
\section{A Simple Example}
|
||||
\label{simpleExample}
|
||||
\section{A Simple Example
|
||||
\label{simpleExample}}
|
||||
|
||||
Let's create an extension module called \samp{spam} (the favorite food
|
||||
of Monty Python fans...) and let's say we want to create a Python
|
||||
|
|
@ -161,8 +161,8 @@ appropriate exception by so the calling function can return
|
|||
\NULL{} immediately (as we saw in the example).
|
||||
|
||||
|
||||
\section{Intermezzo: Errors and Exceptions}
|
||||
\label{errors}
|
||||
\section{Intermezzo: Errors and Exceptions
|
||||
\label{errors}}
|
||||
|
||||
An important convention throughout the Python interpreter is the
|
||||
following: when a function fails, it should set an exception condition
|
||||
|
|
@ -288,8 +288,8 @@ described in the \emph{Python Library Reference} under ``Built-in
|
|||
Exceptions.''
|
||||
|
||||
|
||||
\section{Back to the Example}
|
||||
\label{backToExample}
|
||||
\section{Back to the Example
|
||||
\label{backToExample}}
|
||||
|
||||
Going back to our example function, you should now be able to
|
||||
understand this statement:
|
||||
|
|
@ -344,8 +344,8 @@ returning \ctype{void}), the corresponding Python function must return
|
|||
pointer, which means ``error'' in most contexts, as we have seen.
|
||||
|
||||
|
||||
\section{The Module's Method Table and Initialization Function}
|
||||
\label{methodTable}
|
||||
\section{The Module's Method Table and Initialization Function
|
||||
\label{methodTable}}
|
||||
|
||||
I promised to show how \cfunction{spam_system()} is called from Python
|
||||
programs. First, we need to list its name and address in a ``method
|
||||
|
|
@ -402,8 +402,8 @@ if the module could not be initialized satisfactorily, so the caller
|
|||
doesn't need to check for errors.
|
||||
|
||||
|
||||
\section{Compilation and Linkage}
|
||||
\label{compilation}
|
||||
\section{Compilation and Linkage
|
||||
\label{compilation}}
|
||||
|
||||
There are two more things to do before you can use your new extension:
|
||||
compiling and linking it with the Python system. If you use dynamic
|
||||
|
|
@ -435,8 +435,8 @@ be listed on the line in the configuration file as well, for instance:
|
|||
spam spammodule.o -lX11
|
||||
\end{verbatim}
|
||||
|
||||
\section{Calling Python Functions From \C{}}
|
||||
\label{callingPython}
|
||||
\section{Calling Python Functions from \C{}
|
||||
\label{callingPython}}
|
||||
|
||||
So far we have concentrated on making \C{} functions callable from
|
||||
Python. The reverse is also useful: calling Python functions from \C{}.
|
||||
|
|
@ -450,7 +450,8 @@ Fortunately, the Python interpreter is easily called recursively, and
|
|||
there is a standard interface to call a Python function. (I won't
|
||||
dwell on how to call the Python parser with a particular string as
|
||||
input --- if you're interested, have a look at the implementation of
|
||||
the \samp{-c} command line option in \file{Python/pythonmain.c}.)
|
||||
the \samp{-c} command line option in \file{Python/pythonmain.c} from
|
||||
the Python source code.)
|
||||
|
||||
Calling a Python function is easy. First, the Python program must
|
||||
somehow pass you the Python function object. You should provide a
|
||||
|
|
@ -467,19 +468,37 @@ static PyObject *
|
|||
my_set_callback(dummy, arg)
|
||||
PyObject *dummy, *arg;
|
||||
{
|
||||
Py_XDECREF(my_callback); /* Dispose of previous callback */
|
||||
Py_XINCREF(arg); /* Add a reference to new callback */
|
||||
my_callback = arg; /* Remember new callback */
|
||||
/* Boilerplate to return "None" */
|
||||
Py_INCREF(Py_None);
|
||||
return Py_None;
|
||||
PyObject *result = NULL;
|
||||
PyObject *temp;
|
||||
|
||||
if (PyArg_ParseTuple(args, "O:set_callback", &temp)) {
|
||||
if (!PyCallable_Check(temp)) {
|
||||
PyErr_SetString(PyExc_TypeError, "parameter must be callable");
|
||||
return NULL;
|
||||
}
|
||||
Py_XINCREF(temp); /* Add a reference to new callback */
|
||||
Py_XDECREF(my_callback); /* Dispose of previous callback */
|
||||
my_callback = temp; /* Remember new callback */
|
||||
/* Boilerplate to return "None" */
|
||||
Py_INCREF(Py_None);
|
||||
result = Py_None;
|
||||
}
|
||||
return result;
|
||||
}
|
||||
\end{verbatim}
|
||||
|
||||
This function must be registered with the interpreter using the
|
||||
\constant{METH_VARARGS} flag; this is described in Section
|
||||
\ref{methodTable}, ``The Module's Method Table and Initialization
|
||||
Function.'' The \cfunction{PyArg_ParseTuple()} function and its
|
||||
arguments are documented in Section \ref{parseTuple}, ``Format Strings
|
||||
for \cfunction{PyArg_ParseTuple()}.''
|
||||
|
||||
The macros \cfunction{Py_XINCREF()} and \cfunction{Py_XDECREF()}
|
||||
increment/decrement the reference count of an object and are safe in
|
||||
the presence of \NULL{} pointers. More info on them in the section on
|
||||
Reference Counts below.
|
||||
the presence of \NULL{} pointers (but note that \var{temp} will not be
|
||||
\NULL{} in this context). More info on them in Section
|
||||
\ref{refcounts}, ``Reference Counts.''
|
||||
|
||||
Later, when it is time to call the function, you call the \C{} function
|
||||
\cfunction{PyEval_CallObject()}. This function has two arguments, both
|
||||
|
|
@ -561,8 +580,8 @@ code is not complete: \cfunction{Py_BuildValue()} may run out of
|
|||
memory, and this should be checked.
|
||||
|
||||
|
||||
\section{Format Strings for \cfunction{PyArg_ParseTuple()}}
|
||||
\label{parseTuple}
|
||||
\section{Format Strings for \cfunction{PyArg_ParseTuple()}
|
||||
\label{parseTuple}}
|
||||
|
||||
The \cfunction{PyArg_ParseTuple()} function is declared as follows:
|
||||
|
||||
|
|
@ -767,8 +786,8 @@ Some example calls:
|
|||
\end{verbatim}
|
||||
|
||||
|
||||
\section{Keyword Parsing with \cfunction{PyArg_ParseTupleAndKeywords()}}
|
||||
\label{parseTupleAndKeywords}
|
||||
\section{Keyword Parsing with \cfunction{PyArg_ParseTupleAndKeywords()}
|
||||
\label{parseTupleAndKeywords}}
|
||||
|
||||
The \cfunction{PyArg_ParseTupleAndKeywords()} function is declared as
|
||||
follows:
|
||||
|
|
@ -837,8 +856,8 @@ initkeywdarg()
|
|||
\end{verbatim}
|
||||
|
||||
|
||||
\section{The \cfunction{Py_BuildValue()} Function}
|
||||
\label{buildValue}
|
||||
\section{The \cfunction{Py_BuildValue()} Function
|
||||
\label{buildValue}}
|
||||
|
||||
This function is the counterpart to \cfunction{PyArg_ParseTuple()}. It is
|
||||
declared as follows:
|
||||
|
|
@ -967,8 +986,8 @@ Examples (to the left the call, to the right the resulting Python value):
|
|||
1, 2, 3, 4, 5, 6) (((1, 2), (3, 4)), (5, 6))
|
||||
\end{verbatim}
|
||||
|
||||
\section{Reference Counts}
|
||||
\label{refcounts}
|
||||
\section{Reference Counts
|
||||
\label{refcounts}}
|
||||
|
||||
%\subsection{Introduction}
|
||||
|
||||
|
|
@ -1032,8 +1051,8 @@ Maybe some day a sufficiently portable automatic garbage collector
|
|||
will be available for \C{}. Until then, we'll have to live with
|
||||
reference counts.
|
||||
|
||||
\subsection{Reference Counting in Python}
|
||||
\label{refcountsInPython}
|
||||
\subsection{Reference Counting in Python
|
||||
\label{refcountsInPython}}
|
||||
|
||||
There are two macros, \code{Py_INCREF(x)} and \code{Py_DECREF(x)},
|
||||
which handle the incrementing and decrementing of the reference count.
|
||||
|
|
@ -1080,8 +1099,8 @@ which the reference was borrowed --- it creates a new owned reference,
|
|||
and gives full owner responsibilities (i.e., the new owner must
|
||||
dispose of the reference properly, as well as the previous owner).
|
||||
|
||||
\subsection{Ownership Rules}
|
||||
\label{ownershipRules}
|
||||
\subsection{Ownership Rules
|
||||
\label{ownershipRules}}
|
||||
|
||||
Whenever an object reference is passed into or out of a function, it
|
||||
is part of the function's interface specification whether ownership is
|
||||
|
|
@ -1130,8 +1149,8 @@ The object reference returned from a \C{} function that is called from
|
|||
Python must be an owned reference --- ownership is tranferred from the
|
||||
function to its caller.
|
||||
|
||||
\subsection{Thin Ice}
|
||||
\label{thinIce}
|
||||
\subsection{Thin Ice
|
||||
\label{thinIce}}
|
||||
|
||||
There are a few situations where seemingly harmless use of a borrowed
|
||||
reference can lead to problems. These all have to do with implicit
|
||||
|
|
@ -1212,8 +1231,8 @@ bug(PyObject *list) {
|
|||
}
|
||||
\end{verbatim}
|
||||
|
||||
\subsection{NULL Pointers}
|
||||
\label{nullPointers}
|
||||
\subsection{NULL Pointers
|
||||
\label{nullPointers}}
|
||||
|
||||
In general, functions that take object references as arguments do not
|
||||
expect you to pass them \NULL{} pointers, and will dump core (or
|
||||
|
|
@ -1249,8 +1268,8 @@ It is a severe error to ever let a \NULL{} pointer ``escape'' to
|
|||
the Python user.
|
||||
|
||||
|
||||
\section{Writing Extensions in \Cpp{}}
|
||||
\label{cplusplus}
|
||||
\section{Writing Extensions in \Cpp{}
|
||||
\label{cplusplus}}
|
||||
|
||||
It is possible to write extension modules in \Cpp{}. Some restrictions
|
||||
apply. If the main program (the Python interpreter) is compiled and
|
||||
|
|
@ -1264,8 +1283,8 @@ It is unnecessary to enclose the Python header files in
|
|||
\samp{__cplusplus} is defined (all recent \Cpp{} compilers define this
|
||||
symbol).
|
||||
|
||||
\chapter{Embedding Python in another application}
|
||||
\label{embedding}
|
||||
\chapter{Embedding Python in Another Application
|
||||
\label{embedding}}
|
||||
|
||||
Embedding Python is similar to extending it, but not quite. The
|
||||
difference is that when you extend Python, the main program of the
|
||||
|
|
@ -1293,8 +1312,8 @@ A simple demo of embedding Python can be found in the directory
|
|||
\file{Demo/embed}.
|
||||
|
||||
|
||||
\section{Embedding Python in \Cpp{}}
|
||||
\label{embeddingInCplusplus}
|
||||
\section{Embedding Python in \Cpp{}
|
||||
\label{embeddingInCplusplus}}
|
||||
|
||||
It is also possible to embed Python in a \Cpp{} program; precisely how this
|
||||
is done will depend on the details of the \Cpp{} system used; in general you
|
||||
|
|
@ -1303,8 +1322,8 @@ to compile and link your program. There is no need to recompile Python
|
|||
itself using \Cpp{}.
|
||||
|
||||
|
||||
\chapter{Dynamic Loading}
|
||||
\label{dynload}
|
||||
\chapter{Dynamic Loading
|
||||
\label{dynload}}
|
||||
|
||||
On most modern systems it is possible to configure Python to support
|
||||
dynamic loading of extension modules implemented in \C{}. When shared
|
||||
|
|
@ -1329,15 +1348,15 @@ loading a module that was compiled for a different version of Python
|
|||
(e.g. with a different representation of objects) may dump core.
|
||||
|
||||
|
||||
\section{Configuring and Building the Interpreter for Dynamic Loading}
|
||||
\label{dynloadConfig}
|
||||
\section{Configuring and Building the Interpreter for Dynamic Loading
|
||||
\label{dynloadConfig}}
|
||||
|
||||
There are three styles of dynamic loading: one using shared libraries,
|
||||
one using SGI IRIX 4 dynamic loading, and one using GNU dynamic
|
||||
loading.
|
||||
|
||||
\subsection{Shared Libraries}
|
||||
\label{sharedlibs}
|
||||
\subsection{Shared Libraries
|
||||
\label{sharedlibs}}
|
||||
|
||||
The following systems support dynamic loading using shared libraries:
|
||||
SunOS 4; Solaris 2; SGI IRIX 5 (but not SGI IRIX 4!), Linux, FreeBSD,
|
||||
|
|
@ -1350,8 +1369,8 @@ systems --- the \file{configure} detects the presence of the
|
|||
\code{<dlfcn.h>} header file and automatically configures dynamic
|
||||
loading.
|
||||
|
||||
\subsection{SGI IRIX 4 Dynamic Loading}
|
||||
\label{irixDynload}
|
||||
\subsection{SGI IRIX 4 Dynamic Loading
|
||||
\label{irixDynload}}
|
||||
|
||||
Only SGI IRIX 4 supports dynamic loading of modules using SGI dynamic
|
||||
loading. (SGI IRIX 5 might also support it but it is inferior to
|
||||
|
|
@ -1372,8 +1391,8 @@ pathname of the \code{dl} directory.
|
|||
Now build and install Python as you normally would (see the
|
||||
\file{README} file in the toplevel Python directory.)
|
||||
|
||||
\subsection{GNU Dynamic Loading}
|
||||
\label{gnuDynload}
|
||||
\subsection{GNU Dynamic Loading
|
||||
\label{gnuDynload}}
|
||||
|
||||
GNU dynamic loading supports (according to its \file{README} file) the
|
||||
following hardware and software combinations: VAX (Ultrix), Sun 3
|
||||
|
|
@ -1403,8 +1422,8 @@ of the GNU DLD package. The Python interpreter you build hereafter
|
|||
will support GNU dynamic loading.
|
||||
|
||||
|
||||
\section{Building a Dynamically Loadable Module}
|
||||
\label{makedynload}
|
||||
\section{Building a Dynamically Loadable Module
|
||||
\label{makedynload}}
|
||||
|
||||
Since there are three styles of dynamic loading, there are also three
|
||||
groups of instructions for building a dynamically loadable module.
|
||||
|
|
@ -1424,8 +1443,8 @@ contain the options \samp{-I\$(PYTHONTOP) -I\$(PYTHONTOP)/Include}.
|
|||
\file{config.h} header lives in the toplevel directory.)
|
||||
|
||||
|
||||
\subsection{Shared Libraries}
|
||||
\label{linking}
|
||||
\subsection{Shared Libraries
|
||||
\label{linking}}
|
||||
|
||||
You must link the \file{.o} file to produce a shared library. This is
|
||||
done using a special invocation of the \UNIX{} loader/linker,
|
||||
|
|
@ -1459,8 +1478,8 @@ The resulting file \file{spammodule.so} must be copied into a directory
|
|||
along the Python module search path.
|
||||
|
||||
|
||||
\subsection{SGI IRIX 4 Dynamic Loading}
|
||||
\label{irixLinking}
|
||||
\subsection{SGI IRIX 4 Dynamic Loading
|
||||
\label{irixLinking}}
|
||||
|
||||
\strong{IMPORTANT:} You must compile your extension module with the
|
||||
additional \C{} flag \samp{-G0} (or \samp{-G 0}). This instructs the
|
||||
|
|
@ -1489,8 +1508,8 @@ normally only \samp{-l} options or absolute pathnames of libraries
|
|||
(\samp{.a} files) should be used.
|
||||
|
||||
|
||||
\subsection{GNU Dynamic Loading}
|
||||
\label{gnuLinking}
|
||||
\subsection{GNU Dynamic Loading
|
||||
\label{gnuLinking}}
|
||||
|
||||
Just copy \file{spammodule.o} into a directory along the Python module
|
||||
search path.%
|
||||
|
|
|
|||
Loading…
Reference in New Issue