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<div class="section" id="buffers-and-memoryview-objects">
<span id="bufferobjects"></span><h1>Buffers and Memoryview Objects<a class="headerlink" href="#buffers-and-memoryview-objects" title="Permalink to this headline">¶</a></h1>
<p id="index-0">Python objects implemented in C can export a group of functions called the
“buffer interface.” These functions can be used by an object to expose its
data in a raw, byte-oriented format. Clients of the object can use the buffer
interface to access the object data directly, without needing to copy it
first.</p>
<p>Two examples of objects that support the buffer interface are strings and
arrays. The string object exposes the character contents in the buffer
interface’s byte-oriented form. An array can also expose its contents, but it
should be noted that array elements may be multi-byte values.</p>
<p>An example user of the buffer interface is the file object’s <tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt>
method. Any object that can export a series of bytes through the buffer
interface can be written to a file. There are a number of format codes to
<a href="#id1"><span class="problematic" id="id2">:cfunc:`PyArg_ParseTuple`</span></a> that operate against an object’s buffer interface,
returning data from the target object.</p>
<p>Starting from version 1.6, Python has been providing Python-level buffer
objects and a C-level buffer API so that any built-in or used-defined type can
expose its characteristics. Both, however, have been deprecated because of
various shortcomings, and have been officially removed in Python 3.0 in favour
of a new C-level buffer API and a new Python-level object named
<a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><tt class="xref py py-class docutils literal"><span class="pre">memoryview</span></tt></a>.</p>
<p>The new buffer API has been backported to Python 2.6, and the
<a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><tt class="xref py py-class docutils literal"><span class="pre">memoryview</span></tt></a> object has been backported to Python 2.7. It is strongly
advised to use them rather than the old APIs, unless you are blocked from
doing so for compatibility reasons.</p>
<div class="section" id="the-new-style-py-buffer-struct">
<h2>The new-style Py_buffer struct<a class="headerlink" href="#the-new-style-py-buffer-struct" title="Permalink to this headline">¶</a></h2>
</div>
<div class="section" id="buffer-related-functions">
<h2>Buffer related functions<a class="headerlink" href="#buffer-related-functions" title="Permalink to this headline">¶</a></h2>
</div>
<div class="section" id="memoryview-objects">
<h2>MemoryView objects<a class="headerlink" href="#memoryview-objects" title="Permalink to this headline">¶</a></h2>
<p>A memoryview object is an extended buffer object that could replace the buffer
object (but doesn’t have to as that could be kept as a simple 1-d memoryview
object). It, unlike <a href="#id3"><span class="problematic" id="id4">:ctype:`Py_buffer`</span></a>, is a Python object (exposed as
<a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><tt class="xref py py-class docutils literal"><span class="pre">memoryview</span></tt></a> in <tt class="xref py py-mod docutils literal"><span class="pre">builtins</span></tt>), so it can be used with Python code.</p>
</div>
<div class="section" id="old-style-buffer-objects">
<h2>Old-style buffer objects<a class="headerlink" href="#old-style-buffer-objects" title="Permalink to this headline">¶</a></h2>
<p id="index-1">More information on the old buffer interface is provided in the section
<a class="reference internal" href="typeobj.html#buffer-structs"><em>Buffer Object Structures</em></a>, under the description for <a href="#id5"><span class="problematic" id="id6">:ctype:`PyBufferProcs`</span></a>.</p>
<p>A “buffer object” is defined in the <tt class="file docutils literal"><span class="pre">bufferobject.h</span></tt> header (included by
<tt class="file docutils literal"><span class="pre">Python.h</span></tt>). These objects look very similar to string objects at the
Python programming level: they support slicing, indexing, concatenation, and
some other standard string operations. However, their data can come from one
of two sources: from a block of memory, or from another object which exports
the buffer interface.</p>
<p>Buffer objects are useful as a way to expose the data from another object’s
buffer interface to the Python programmer. They can also be used as a
zero-copy slicing mechanism. Using their ability to reference a block of
memory, it is possible to expose any data to the Python programmer quite
easily. The memory could be a large, constant array in a C extension, it could
be a raw block of memory for manipulation before passing to an operating
system library, or it could be used to pass around structured data in its
native, in-memory format.</p>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Buffers and Memoryview Objects</a><ul>
<li><a class="reference internal" href="#the-new-style-py-buffer-struct">The new-style Py_buffer struct</a></li>
<li><a class="reference internal" href="#buffer-related-functions">Buffer related functions</a></li>
<li><a class="reference internal" href="#memoryview-objects">MemoryView objects</a></li>
<li><a class="reference internal" href="#old-style-buffer-objects">Old-style buffer objects</a></li>
</ul>
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