[Python-checkins] bpo-27867: Add a porting guide for PySlice_GetIndicesEx(). (#1973)
Serhiy Storchaka
webhook-mailer at python.org
Sun Oct 8 05:53:36 EDT 2017
https://github.com/python/cpython/commit/4d3f084c035ad3dfd9f8479886c41b1b1823ace2
commit: 4d3f084c035ad3dfd9f8479886c41b1b1823ace2
branch: master
author: Serhiy Storchaka <storchaka at gmail.com>
committer: GitHub <noreply at github.com>
date: 2017-10-08T12:53:34+03:00
summary:
bpo-27867: Add a porting guide for PySlice_GetIndicesEx(). (#1973)
files:
M Doc/c-api/slice.rst
M Doc/whatsnew/3.7.rst
diff --git a/Doc/c-api/slice.rst b/Doc/c-api/slice.rst
index f8395ec8d77..8ad9a29b256 100644
--- a/Doc/c-api/slice.rst
+++ b/Doc/c-api/slice.rst
@@ -53,6 +53,22 @@ Slice Objects
Returns ``0`` on success and ``-1`` on error with exception set.
+ .. note::
+ This function is considered not safe for resizable sequences.
+ Its invocation should be replaced by a combination of
+ :c:func:`PySlice_Unpack` and :c:func:`PySlice_AdjustIndices` where ::
+
+ if (PySlice_GetIndicesEx(slice, length, &start, &stop, &step, &slicelength) < 0) {
+ // return error
+ }
+
+ is replaced by ::
+
+ if (PySlice_Unpack(slice, &start, &stop, &step) < 0) {
+ // return error
+ }
+ slicelength = PySlice_AdjustIndices(length, &start, &stop, step);
+
.. versionchanged:: 3.2
The parameter type for the *slice* parameter was ``PySliceObject*``
before.
@@ -61,7 +77,7 @@ Slice Objects
If ``Py_LIMITED_API`` is not set or set to the value between ``0x03050400``
and ``0x03060000`` (not including) or ``0x03060100`` or higher
:c:func:`!PySlice_GetIndicesEx` is implemented as a macro using
- :c:func:`PySlice_Unpack` and :c:func:`PySlice_AdjustIndices`.
+ :c:func:`!PySlice_Unpack` and :c:func:`!PySlice_AdjustIndices`.
Arguments *start*, *stop* and *step* are evaluated more than once.
.. deprecated:: 3.6.1
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
index 24a1dc4d13b..a0c20a0ad88 100644
--- a/Doc/whatsnew/3.7.rst
+++ b/Doc/whatsnew/3.7.rst
@@ -581,6 +581,19 @@ Changes in the Python API
in the output. (Contributed by Utkarsh Upadhyay in :issue:`30302`.)
+Changes in the C API
+--------------------
+
+* The function :c:func:`PySlice_GetIndicesEx` is considered not safe for
+ resizable sequences. If the slice indices are not instances of :class:`int`,
+ but objects that implement the :meth:`!__index__` method, the sequence can be
+ resized after passing its length to :c:func:`!PySlice_GetIndicesEx`. This
+ can lead to returning indices out of the length of the sequence. For
+ avoiding possible problems use new functions :c:func:`PySlice_Unpack` and
+ :c:func:`PySlice_AdjustIndices`.
+ (Contributed by Serhiy Storchaka in :issue:`27867`.)
+
+
CPython bytecode changes
------------------------
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