[Python-checkins] r82842 - python/branches/py3k/Doc/library/stdtypes.rst
antoine.pitrou
python-checkins at python.org
Mon Jul 12 22:01:53 CEST 2010
Author: antoine.pitrou
Date: Mon Jul 12 22:01:52 2010
New Revision: 82842
Log:
Fix definition of len() and indexing for memoryview objects (part of #7696).
Modified:
python/branches/py3k/Doc/library/stdtypes.rst
Modified: python/branches/py3k/Doc/library/stdtypes.rst
==============================================================================
--- python/branches/py3k/Doc/library/stdtypes.rst (original)
+++ python/branches/py3k/Doc/library/stdtypes.rst Mon Jul 12 22:01:52 2010
@@ -2264,10 +2264,19 @@
buffer protocol. Builtin objects that support the buffer protocol include
:class:`bytes` and :class:`bytearray`.
- ``len(view)`` returns the total number of bytes in the memoryview, *view*.
+ A :class:`memoryview` has the notion of an *element*, which is the
+ atomic memory unit handled by the originating object *obj*. For many
+ simple types such as :class:`bytes` and :class:`bytearray`, an element
+ is a single byte, but other types such as :class:`array.array` may have
+ bigger elements.
+
+ ``len(view)`` returns the total number of elements in the memoryview,
+ *view*. The :class:`~memoryview.itemsize` attribute will give you the
+ number of bytes in a single element.
A :class:`memoryview` supports slicing to expose its data. Taking a single
- index will return a single byte. Full slicing will result in a subview::
+ index will return a single element as a :class:`bytes` object. Full
+ slicing will result in a subview::
>>> v = memoryview(b'abcefg')
>>> v[1]
@@ -2278,11 +2287,8 @@
<memory at 0x77ab28>
>>> bytes(v[1:4])
b'bce'
- >>> v[3:-1]
- <memory at 0x744f18>
- >>> bytes(v[4:-1])
- If the object the memory view is over supports changing its data, the
+ If the object the memoryview is over supports changing its data, the
memoryview supports slice assignment::
>>> data = bytearray(b'abcefg')
@@ -2302,12 +2308,18 @@
Notice how the size of the memoryview object cannot be changed.
-
:class:`memoryview` has two methods:
.. method:: tobytes()
- Return the data in the buffer as a bytestring.
+ Return the data in the buffer as a bytestring. This is equivalent to
+ calling the :class:`bytes` constructor on the memoryview. ::
+
+ >>> m = memoryview(b"abc")
+ >>> m.tobytes()
+ b'abc'
+ >>> bytes(m)
+ b'abc'
.. method:: tolist()
@@ -2325,7 +2337,15 @@
.. attribute:: itemsize
- The size in bytes of each element of the memoryview.
+ The size in bytes of each element of the memoryview::
+
+ >>> m = memoryview(array.array('H', [1,2,3]))
+ >>> m.itemsize
+ 2
+ >>> m[0]
+ b'\x01\x00'
+ >>> len(m[0]) == m.itemsize
+ True
.. attribute:: shape
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