Added optional None arguments to itertools.islice().
diff --git a/Doc/lib/libitertools.tex b/Doc/lib/libitertools.tex
index be53015..fbde69d 100644
--- a/Doc/lib/libitertools.tex
+++ b/Doc/lib/libitertools.tex
@@ -261,6 +261,11 @@
yield element
next += step
\end{verbatim}
+
+ If \var{start} is \code{None}, then iteration starts at zero.
+ If \var{step} is \code{None}, then the step defaults to one.
+ \versionchanged[accept \code{None} values for default \var{start} and
+ \var{step}]{2.5}
\end{funcdesc}
\begin{funcdesc}{izip}{*iterables}
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 0f74c62..becb3b2 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -260,6 +260,8 @@
# Test stop=None
self.assertEqual(list(islice(xrange(10), None)), range(10))
+ self.assertEqual(list(islice(xrange(10), None, None)), range(10))
+ self.assertEqual(list(islice(xrange(10), None, None, None)), range(10))
self.assertEqual(list(islice(xrange(10), 2, None)), range(2, 10))
self.assertEqual(list(islice(xrange(10), 1, None, 2)), range(1, 10, 2))
diff --git a/Misc/NEWS b/Misc/NEWS
index 235c257..95b9d2c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -17,6 +17,10 @@
Extension Modules
-----------------
+- itertools.islice() now accepts None for the start and step arguments.
+ This allows islice() to work more readily with slices:
+ islice(s.start, s.stop, s.step)
+
Library
-------
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index bf148ac..31ba13a 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -1044,14 +1044,14 @@
{
PyObject *seq;
long start=0, stop=-1, step=1;
- PyObject *it, *a1=NULL, *a2=NULL;
+ PyObject *it, *a1=NULL, *a2=NULL, *a3=NULL;
int numargs;
isliceobject *lz;
- numargs = PyTuple_Size(args);
- if (!PyArg_ParseTuple(args, "OO|Ol:islice", &seq, &a1, &a2, &step))
+ if (!PyArg_UnpackTuple(args, "islice", 2, 4, &seq, &a1, &a2, &a3))
return NULL;
+ numargs = PyTuple_Size(args);
if (numargs == 2) {
if (a1 != Py_None) {
stop = PyInt_AsLong(a1);
@@ -1059,39 +1059,41 @@
if (PyErr_Occurred())
PyErr_Clear();
PyErr_SetString(PyExc_ValueError,
- "Stop argument must be a non-negative integer or None.");
+ "Stop argument for islice() must be a non-negative integer or None.");
return NULL;
}
}
} else {
- start = PyInt_AsLong(a1);
- if (start == -1 && PyErr_Occurred()) {
+ if (a1 != Py_None)
+ start = PyInt_AsLong(a1);
+ if (start == -1 && PyErr_Occurred())
PyErr_Clear();
- PyErr_SetString(PyExc_ValueError,
- "Start argument must be a non-negative integer.");
- return NULL;
- }
if (a2 != Py_None) {
stop = PyInt_AsLong(a2);
if (stop == -1) {
if (PyErr_Occurred())
PyErr_Clear();
PyErr_SetString(PyExc_ValueError,
- "Stop argument must be a non-negative integer or None.");
+ "Stop argument for islice() must be a non-negative integer or None.");
return NULL;
}
}
}
-
if (start<0 || stop<-1) {
PyErr_SetString(PyExc_ValueError,
- "Indices for islice() must be non-negative integers.");
+ "Indices for islice() must be non-negative integers or None.");
return NULL;
}
+ if (a3 != NULL) {
+ if (a3 != Py_None)
+ step = PyInt_AsLong(a3);
+ if (step == -1 && PyErr_Occurred())
+ PyErr_Clear();
+ }
if (step<1) {
PyErr_SetString(PyExc_ValueError,
- "Step must be one or larger for islice().");
+ "Step for islice() must be a positive integer or None.");
return NULL;
}