Bug #1541682: Fix example in the "Refcount details" API docs.
Additionally, remove a faulty example showing PySequence_SetItem applied
to a newly created list object and add notes that this isn't a good idea.
(backport from rev. 51364)
diff --git a/Doc/api/intro.tex b/Doc/api/intro.tex
index 1295e5f..80650fe 100644
--- a/Doc/api/intro.tex
+++ b/Doc/api/intro.tex
@@ -225,25 +225,10 @@
\cfunction{PyTuple_SetItem()} for tuples that you are creating
yourself.
-Equivalent code for populating a list can be written using
-\cfunction{PyList_New()} and \cfunction{PyList_SetItem()}. Such code
-can also use \cfunction{PySequence_SetItem()}; this illustrates the
-difference between the two (the extra \cfunction{Py_DECREF()} calls):
+Equivalent code for populating a list can be written using
+\cfunction{PyList_New()} and \cfunction{PyList_SetItem()}.
-\begin{verbatim}
-PyObject *l, *x;
-
-l = PyList_New(3);
-x = PyInt_FromLong(1L);
-PySequence_SetItem(l, 0, x); Py_DECREF(x);
-x = PyInt_FromLong(2L);
-PySequence_SetItem(l, 1, x); Py_DECREF(x);
-x = PyString_FromString("three");
-PySequence_SetItem(l, 2, x); Py_DECREF(x);
-\end{verbatim}
-
-You might find it strange that the ``recommended'' approach takes more
-code. However, in practice, you will rarely use these ways of
+However, in practice, you will rarely use these ways of
creating and populating a tuple or list. There's a generic function,
\cfunction{Py_BuildValue()}, that can create most common objects from
C values, directed by a \dfn{format string}. For example, the
@@ -251,10 +236,10 @@
also takes care of the error checking):
\begin{verbatim}
-PyObject *t, *l;
+PyObject *tuple, *list;
-t = Py_BuildValue("(iis)", 1, 2, "three");
-l = Py_BuildValue("[iis]", 1, 2, "three");
+tuple = Py_BuildValue("(iis)", 1, 2, "three");
+list = Py_BuildValue("[iis]", 1, 2, "three");
\end{verbatim}
It is much more common to use \cfunction{PyObject_SetItem()} and
@@ -276,8 +261,12 @@
if (n < 0)
return -1;
for (i = 0; i < n; i++) {
- if (PyObject_SetItem(target, i, item) < 0)
+ PyObject *index = PyInt_FromLong(i);
+ if (!index)
return -1;
+ if (PyObject_SetItem(target, index, item) < 0)
+ return -1;
+ Py_DECREF(index);
}
return 0;
}