Added description of "D" format for PyArg_ParseTuple(), including example
use with function name provided as well. Wrapped up PyArg_ParseTupleAndKeywords() description and provided example based on Geoff Philbrick's example to the mailing list.
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Fred Drake
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Doc/ext.tex
89
Doc/ext.tex
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@ -356,14 +356,17 @@ function. It should normally always be \samp{METH_VARARGS} or
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\samp{METH_VARARGS | METH_KEYWORDS}; a value of \samp{0} means that an
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obsolete variant of \code{PyArg_ParseTuple()} is used.
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When using only \samp{METH_VARARGS}, the function should expect
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the Python-level parameters to be passed in as a tuple acceptable for
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parsing via \cfunction{PyArg_ParseTuple()}; more information on this
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function is provided below.
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The \code{METH_KEYWORDS} bit may be set in the third field if keyword
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arguments should be passed to the function. In this case, the \C{}
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function should accept a third \samp{PyObject *} parameter which will
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be a dictionary of keywords. Use \code{PyArg_ParseTupleAndKeywords()}
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to parse the arguemts to such a function.
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XXX --- need to explain PyArg_ParseTupleAndKeywords() in detail.
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The method table must be passed to the interpreter in the module's
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initialization function (which should be the only non-\code{static}
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item defined in the module file):
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@ -621,6 +624,9 @@ Convert a Python floating point number to a \C{} \code{float}.
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\item[\samp{d} (float) {[double]}]
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Convert a Python floating point number to a \C{} \code{double}.
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\item[\samp{D} (complex) {[Py_complex]}]
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Convert a Python complex number to a \C{} \code{Py_complex} structure.
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\item[\samp{O} (object) {[PyObject *]}]
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Store a Python object (without any conversion) in a \C{} object pointer.
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The \C{} program thus receives the actual object that was passed. The
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@ -736,8 +742,85 @@ Some example calls:
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/* Possible Python call:
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f(((0, 0), (400, 300)), (10, 10)) */
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}
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{
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Py_complex c;
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ok = PyArg_ParseTuple(args, "D:myfunction", &c);
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/* a complex, also providing a function name for errors */
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/* Possible Python call: myfunction(1+2j) */
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}
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\end{verbatim}
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%
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\section{Keyword Parsing with \sectcode{PyArg_ParseTupleAndKeywords()}}
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The \cfunction{PyArg_ParseTupleAndKeywords()} function is declared as
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follows:
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\bcode\begin{verbatim}
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int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict,
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char *format, char **kwlist, ...);
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\end{verbatim}\ecode
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The \var{arg} and \var{format} parameters are identical to those of the
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\cfunction{PyArg_ParseTuple()} function. The \var{kwdict} parameter
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is the dictionary of keywords received as the third parameter from the
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Python runtime. The \var{kwlist} parameter is a \NULL{}-terminated
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list of strings which identify the parameters; the names are matched
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with the type information from \var{format} from left to right.
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\strong{Note:} Nested tuples cannot be parsed when using keyword
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arguments! Keyword parameters passed in which are not present in the
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\var{kwlist} will cause a \exception{TypeError} to be raised.
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Here is an example module which uses keywords, based on an example by
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Geoff Philbrick (\email{philbrick@hks.com}):
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\begin{verbatim}
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#include <stdio.h>
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#include "Python.h"
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static PyObject *
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keywdarg_parrot(self, args, keywds)
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PyObject *self;
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PyObject *args;
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PyObject *keywds;
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{
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int voltage;
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char *state = "a stiff";
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char *action = "voom";
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char *type = "Norwegian Blue";
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static char *kwlist[] = {"voltage", "state", "action", "type", NULL};
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if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|sss", kwlist,
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&voltage, &state, &action, &type))
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return NULL;
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printf("-- This parrot wouldn't %s if you put %i Volts through it.\n",
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action, voltage);
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printf("-- Lovely plumage, the %s -- It's %s!\n", type, state);
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Py_INCREF(Py_None);
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return Py_None;
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}
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static PyMethodDef keywdarg_methods[] = {
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{"parrot", (PyCFunction)keywdarg_parrot, METH_VARARGS|METH_KEYWORDS},
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{NULL, NULL} /* sentinel */
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};
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void
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initkeywdarg()
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{
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/* Create the module and add the functions */
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Py_InitModule("keywdarg", keywdarg_methods);
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}
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\end{verbatim}
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\section{The \sectcode{Py_BuildValue()} Function}
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This function is the counterpart to \code{PyArg_ParseTuple()}. It is
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@ -356,14 +356,17 @@ function. It should normally always be \samp{METH_VARARGS} or
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\samp{METH_VARARGS | METH_KEYWORDS}; a value of \samp{0} means that an
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obsolete variant of \code{PyArg_ParseTuple()} is used.
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When using only \samp{METH_VARARGS}, the function should expect
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the Python-level parameters to be passed in as a tuple acceptable for
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parsing via \cfunction{PyArg_ParseTuple()}; more information on this
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function is provided below.
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The \code{METH_KEYWORDS} bit may be set in the third field if keyword
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arguments should be passed to the function. In this case, the \C{}
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function should accept a third \samp{PyObject *} parameter which will
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be a dictionary of keywords. Use \code{PyArg_ParseTupleAndKeywords()}
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to parse the arguemts to such a function.
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XXX --- need to explain PyArg_ParseTupleAndKeywords() in detail.
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The method table must be passed to the interpreter in the module's
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initialization function (which should be the only non-\code{static}
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item defined in the module file):
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@ -621,6 +624,9 @@ Convert a Python floating point number to a \C{} \code{float}.
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\item[\samp{d} (float) {[double]}]
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Convert a Python floating point number to a \C{} \code{double}.
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\item[\samp{D} (complex) {[Py_complex]}]
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Convert a Python complex number to a \C{} \code{Py_complex} structure.
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\item[\samp{O} (object) {[PyObject *]}]
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Store a Python object (without any conversion) in a \C{} object pointer.
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The \C{} program thus receives the actual object that was passed. The
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@ -736,8 +742,85 @@ Some example calls:
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/* Possible Python call:
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f(((0, 0), (400, 300)), (10, 10)) */
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}
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{
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Py_complex c;
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ok = PyArg_ParseTuple(args, "D:myfunction", &c);
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/* a complex, also providing a function name for errors */
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/* Possible Python call: myfunction(1+2j) */
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}
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\end{verbatim}
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%
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\section{Keyword Parsing with \sectcode{PyArg_ParseTupleAndKeywords()}}
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The \cfunction{PyArg_ParseTupleAndKeywords()} function is declared as
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follows:
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\bcode\begin{verbatim}
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int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict,
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char *format, char **kwlist, ...);
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\end{verbatim}\ecode
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The \var{arg} and \var{format} parameters are identical to those of the
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\cfunction{PyArg_ParseTuple()} function. The \var{kwdict} parameter
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is the dictionary of keywords received as the third parameter from the
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Python runtime. The \var{kwlist} parameter is a \NULL{}-terminated
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list of strings which identify the parameters; the names are matched
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with the type information from \var{format} from left to right.
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\strong{Note:} Nested tuples cannot be parsed when using keyword
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arguments! Keyword parameters passed in which are not present in the
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\var{kwlist} will cause a \exception{TypeError} to be raised.
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Here is an example module which uses keywords, based on an example by
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Geoff Philbrick (\email{philbrick@hks.com}):
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\begin{verbatim}
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#include <stdio.h>
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#include "Python.h"
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static PyObject *
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keywdarg_parrot(self, args, keywds)
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PyObject *self;
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PyObject *args;
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PyObject *keywds;
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{
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int voltage;
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char *state = "a stiff";
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char *action = "voom";
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char *type = "Norwegian Blue";
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static char *kwlist[] = {"voltage", "state", "action", "type", NULL};
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if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|sss", kwlist,
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&voltage, &state, &action, &type))
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return NULL;
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printf("-- This parrot wouldn't %s if you put %i Volts through it.\n",
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action, voltage);
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printf("-- Lovely plumage, the %s -- It's %s!\n", type, state);
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Py_INCREF(Py_None);
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return Py_None;
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}
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static PyMethodDef keywdarg_methods[] = {
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{"parrot", (PyCFunction)keywdarg_parrot, METH_VARARGS|METH_KEYWORDS},
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{NULL, NULL} /* sentinel */
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};
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void
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initkeywdarg()
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{
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/* Create the module and add the functions */
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Py_InitModule("keywdarg", keywdarg_methods);
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}
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\end{verbatim}
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\section{The \sectcode{Py_BuildValue()} Function}
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This function is the counterpart to \code{PyArg_ParseTuple()}. It is
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