Bug 1003935: xrange overflows
Added XXX comment about why the undocumented PyRange_New() API function
is too broken to be worth the considerable pain of repairing.
Changed range_new() to stop using PyRange_New(). This fixes a variety
of bogus errors. Nothing in the core uses PyRange_New() now.
Documented that xrange() is intended to be simple and fast, and that
CPython restricts its arguments, and length of its result sequence, to
native C longs.
Added some tests that failed before the patch, and repaired a test that
relied on a bogus OverflowError getting raised.
diff --git a/Doc/lib/libfuncs.tex b/Doc/lib/libfuncs.tex
index 062e3e8..1d4df67 100644
--- a/Doc/lib/libfuncs.tex
+++ b/Doc/lib/libfuncs.tex
@@ -79,7 +79,7 @@
\indexii{Boolean}{type}
\versionadded{2.2.1}
- \versionchanged[If no argument is given, this function returns
+ \versionchanged[If no argument is given, this function returns
\constant{False}]{2.3}
\end{funcdesc}
@@ -379,7 +379,7 @@
that differentiate between binary and text files (else it is
ignored). If the file cannot be opened, \exception{IOError} is
raised.
-
+
In addition to the standard \cfunction{fopen()} values \var{mode}
may be \code{'U'} or \code{'rU'}. If Python is built with universal
newline support (the default) the file is opened as a text file, but
@@ -392,7 +392,7 @@
\var{mode} \code{'U'} is the same as normal text mode. Note that
file objects so opened also have an attribute called
\member{newlines} which has a value of \code{None} (if no newlines
- have yet been seen), \code{'\e n'}, \code{'\e r'}, \code{'\e r\e n'},
+ have yet been seen), \code{'\e n'}, \code{'\e r'}, \code{'\e r\e n'},
or a tuple containing all the newline types seen.
If \var{mode} is omitted, it defaults to \code{'r'}. When opening a
@@ -459,7 +459,7 @@
the inner sets should also be \class{frozenset} objects. If
\var{iterable} is not specified, returns a new empty set,
\code{frozenset([])}.
- \versionadded{2.4}
+ \versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{getattr}{object, name\optional{, default}}
@@ -659,7 +659,7 @@
\end{funcdesc}
\begin{funcdesc}{object}{}
- Return a new featureless object. \function{object()} is a base
+ Return a new featureless object. \function{object()} is a base
for all new style classes. It has the methods that are common
to all instances of new style classes.
\versionadded{2.2}
@@ -901,7 +901,7 @@
must be immutable. To represent sets of sets, the inner sets should
be \class{frozenset} objects. If \var{iterable} is not specified,
returns a new empty set, \code{set([])}.
- \versionadded{2.4}
+ \versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{setattr}{object, name, value}
@@ -931,7 +931,7 @@
Return a new sorted list from the items in \var{iterable}.
The optional arguments \var{cmp}, \var{key}, and \var{reverse}
have the same meaning as those for the \method{list.sort()} method.
- \versionadded{2.4}
+ \versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{staticmethod}{function}
@@ -1099,6 +1099,12 @@
them) except when a very large range is used on a memory-starved
machine or when all of the range's elements are never used (such as
when the loop is usually terminated with \keyword{break}).
+
+ \note{\function{xrange()} is intended to be simple and fast.
+ Implementations may impose restrictions to achieve this.
+ The C implementation of Python restricts all arguments to
+ native C longs ("short" Python integers), and also requires
+ that that number of elements fit in a native C long.}
\end{funcdesc}
\begin{funcdesc}{zip}{\optional{seq1, \moreargs}}
@@ -1114,11 +1120,11 @@
\versionchanged[Formerly, \function{zip()} required at least one argument
and \code{zip()} raised a \exception{TypeError} instead of returning
- an empty list.]{2.4}
+ an empty list.]{2.4}
\end{funcdesc}
-% ---------------------------------------------------------------------------
+% ---------------------------------------------------------------------------
\section{Non-essential Built-in Functions \label{non-essential-built-in-funcs}}
diff --git a/Lib/test/test_xrange.py b/Lib/test/test_xrange.py
index ce5284d..f33373e 100644
--- a/Lib/test/test_xrange.py
+++ b/Lib/test/test_xrange.py
@@ -48,10 +48,15 @@
self.assertRaises(TypeError, xrange, 0, "spam")
self.assertRaises(TypeError, xrange, 0, 42, "spam")
- self.assertRaises(OverflowError, xrange, 0, sys.maxint, sys.maxint-1)
+ self.assertEqual(len(xrange(0, sys.maxint, sys.maxint-1)), 2)
+
self.assertRaises(OverflowError, xrange, -sys.maxint, sys.maxint)
self.assertRaises(OverflowError, xrange, 0, 2*sys.maxint)
+ self.assertEqual(len(xrange(-sys.maxint, sys.maxint, 2)),
+ sys.maxint)
+ self.assertRaises(OverflowError, xrange, -sys.maxint-1, sys.maxint, 2)
+
def test_main():
test.test_support.run_unittest(XrangeTest)
diff --git a/Objects/rangeobject.c b/Objects/rangeobject.c
index dbfab9f..dabb8d4 100644
--- a/Objects/rangeobject.c
+++ b/Objects/rangeobject.c
@@ -9,6 +9,13 @@
long len;
} rangeobject;
+/* XXX PyRange_New should be deprecated. It's not documented. It's not
+ * used in the core. Its error-checking is akin to Swiss cheese: accepts
+ * step == 0; accepts len < 0; ignores that (len - 1) * step may overflow;
+ * raises a baffling "integer addition" exception if it thinks the last
+ * item is "too big"; and doesn't compute whether "last item is too big"
+ * correctly even if the multiplication doesn't overflow.
+ */
PyObject *
PyRange_New(long start, long len, long step, int reps)
{
@@ -79,6 +86,7 @@
static PyObject *
range_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
+ rangeobject *obj;
long ilow = 0, ihigh = 0, istep = 1;
long n;
@@ -107,7 +115,14 @@
"xrange() result has too many items");
return NULL;
}
- return PyRange_New(ilow, n, istep, 1);
+
+ obj = PyObject_New(rangeobject, &PyRange_Type);
+ if (obj == NULL)
+ return NULL;
+ obj->start = ilow;
+ obj->len = n;
+ obj->step = istep;
+ return (PyObject *) obj;
}
PyDoc_STRVAR(range_doc,