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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 only expose its contents via the
old-style buffer interface. This limitation does not apply to Python 3,
where <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate"><span class="pre">memoryview</span></code></a> objects can be constructed from arrays, too.
Array elements may be multi-byte values.</p>
<p>An example user of the buffer interface is the file object’s <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code>
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 class="reference internal" href="arg.html#c.PyArg_ParseTuple" title="PyArg_ParseTuple"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyArg_ParseTuple()</span></code></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 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"><code class="xref py py-class docutils literal notranslate"><span class="pre">memoryview</span></code></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"><code class="xref py py-class docutils literal notranslate"><span class="pre">memoryview</span></code></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>
<dl class="type">
<dt id="c.Py_buffer">
<code class="descname">Py_buffer</code><a class="headerlink" href="#c.Py_buffer" title="Permalink to this definition">¶</a></dt>
<dd><dl class="member">
<dt id="c.Py_buffer.buf">
void *<code class="descname">buf</code><a class="headerlink" href="#c.Py_buffer.buf" title="Permalink to this definition">¶</a></dt>
<dd><p>A pointer to the start of the memory for the object.</p>
</dd></dl>
<dl class="member">
<dt>
Py_ssize_t <code class="descname">len</code></dt>
<dd><p>The total length of the memory in bytes.</p>
</dd></dl>
<dl class="member">
<dt id="c.Py_buffer.readonly">
int <code class="descname">readonly</code><a class="headerlink" href="#c.Py_buffer.readonly" title="Permalink to this definition">¶</a></dt>
<dd><p>An indicator of whether the buffer is read only.</p>
</dd></dl>
<dl class="member">
<dt>
const char *<code class="descname">format</code></dt>
<dd><p>A <em>NULL</em> terminated string in <a class="reference internal" href="../library/struct.html#module-struct" title="struct: Interpret strings as packed binary data."><code class="xref py py-mod docutils literal notranslate"><span class="pre">struct</span></code></a> module style syntax giving
the contents of the elements available through the buffer. If this is
<em>NULL</em>, <code class="docutils literal notranslate"><span class="pre">"B"</span></code> (unsigned bytes) is assumed.</p>
</dd></dl>
<dl class="member">
<dt id="c.Py_buffer.ndim">
int <code class="descname">ndim</code><a class="headerlink" href="#c.Py_buffer.ndim" title="Permalink to this definition">¶</a></dt>
<dd><p>The number of dimensions the memory represents as a multi-dimensional
array. If it is <code class="docutils literal notranslate"><span class="pre">0</span></code>, <code class="xref c c-data docutils literal notranslate"><span class="pre">strides</span></code> and <code class="xref c c-data docutils literal notranslate"><span class="pre">suboffsets</span></code> must be
<em>NULL</em>.</p>
</dd></dl>
<dl class="member">
<dt id="c.Py_buffer.shape">
Py_ssize_t *<code class="descname">shape</code><a class="headerlink" href="#c.Py_buffer.shape" title="Permalink to this definition">¶</a></dt>
<dd><p>An array of <code class="xref c c-type docutils literal notranslate"><span class="pre">Py_ssize_t</span></code>s the length of <code class="xref c c-data docutils literal notranslate"><span class="pre">ndim</span></code> giving the
shape of the memory as a multi-dimensional array. Note that
<code class="docutils literal notranslate"><span class="pre">((*shape)[0]</span> <span class="pre">*</span> <span class="pre">...</span> <span class="pre">*</span> <span class="pre">(*shape)[ndims-1])*itemsize</span></code> should be equal to
<code class="xref c c-data docutils literal notranslate"><span class="pre">len</span></code>.</p>
</dd></dl>
<dl class="member">
<dt id="c.Py_buffer.strides">
Py_ssize_t *<code class="descname">strides</code><a class="headerlink" href="#c.Py_buffer.strides" title="Permalink to this definition">¶</a></dt>
<dd><p>An array of <code class="xref c c-type docutils literal notranslate"><span class="pre">Py_ssize_t</span></code>s the length of <code class="xref c c-data docutils literal notranslate"><span class="pre">ndim</span></code> giving the
number of bytes to skip to get to a new element in each dimension.</p>
</dd></dl>
<dl class="member">
<dt id="c.Py_buffer.suboffsets">
Py_ssize_t *<code class="descname">suboffsets</code><a class="headerlink" href="#c.Py_buffer.suboffsets" title="Permalink to this definition">¶</a></dt>
<dd><p>An array of <code class="xref c c-type docutils literal notranslate"><span class="pre">Py_ssize_t</span></code>s the length of <code class="xref c c-data docutils literal notranslate"><span class="pre">ndim</span></code>. If these
suboffset numbers are greater than or equal to 0, then the value stored
along the indicated dimension is a pointer and the suboffset value
dictates how many bytes to add to the pointer after de-referencing. A
suboffset value that it negative indicates that no de-referencing should
occur (striding in a contiguous memory block).</p>
<p>If all suboffsets are negative (i.e. no de-referencing is needed), then
this field must be NULL (the default value).</p>
<p>Here is a function that returns a pointer to the element in an N-D array
pointed to by an N-dimensional index when there are both non-NULL strides
and suboffsets:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span> <span class="o">*</span><span class="nf">get_item_pointer</span><span class="p">(</span><span class="kt">int</span> <span class="n">ndim</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="n">buf</span><span class="p">,</span> <span class="n">Py_ssize_t</span> <span class="o">*</span><span class="n">strides</span><span class="p">,</span>
<span class="n">Py_ssize_t</span> <span class="o">*</span><span class="n">suboffsets</span><span class="p">,</span> <span class="n">Py_ssize_t</span> <span class="o">*</span><span class="n">indices</span><span class="p">)</span> <span class="p">{</span>
<span class="kt">char</span> <span class="o">*</span><span class="n">pointer</span> <span class="o">=</span> <span class="p">(</span><span class="kt">char</span><span class="o">*</span><span class="p">)</span><span class="n">buf</span><span class="p">;</span>
<span class="kt">int</span> <span class="n">i</span><span class="p">;</span>
<span class="k">for</span> <span class="p">(</span><span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">ndim</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
<span class="n">pointer</span> <span class="o">+=</span> <span class="n">strides</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">*</span> <span class="n">indices</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<span class="k">if</span> <span class="p">(</span><span class="n">suboffsets</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">>=</span><span class="mi">0</span> <span class="p">)</span> <span class="p">{</span>
<span class="n">pointer</span> <span class="o">=</span> <span class="o">*</span><span class="p">((</span><span class="kt">char</span><span class="o">**</span><span class="p">)</span><span class="n">pointer</span><span class="p">)</span> <span class="o">+</span> <span class="n">suboffsets</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="k">return</span> <span class="p">(</span><span class="kt">void</span><span class="o">*</span><span class="p">)</span><span class="n">pointer</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
</dd></dl>
<dl class="member">
<dt id="c.Py_buffer.itemsize">
Py_ssize_t <code class="descname">itemsize</code><a class="headerlink" href="#c.Py_buffer.itemsize" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a storage for the itemsize (in bytes) of each element of the
shared memory. It is technically un-necessary as it can be obtained
using <a class="reference internal" href="#c.PyBuffer_SizeFromFormat" title="PyBuffer_SizeFromFormat"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_SizeFromFormat()</span></code></a>, however an exporter may know
this information without parsing the format string and it is necessary
to know the itemsize for proper interpretation of striding. Therefore,
storing it is more convenient and faster.</p>
</dd></dl>
<dl class="member">
<dt id="c.Py_buffer.internal">
void *<code class="descname">internal</code><a class="headerlink" href="#c.Py_buffer.internal" title="Permalink to this definition">¶</a></dt>
<dd><p>This is for use internally by the exporting object. For example, this
might be re-cast as an integer by the exporter and used to store flags
about whether or not the shape, strides, and suboffsets arrays must be
freed when the buffer is released. The consumer should never alter this
value.</p>
</dd></dl>
</dd></dl>
</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>
<dl class="function">
<dt id="c.PyObject_CheckBuffer">
int <code class="descname">PyObject_CheckBuffer</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_CheckBuffer" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">1</span></code> if <em>obj</em> supports the buffer interface otherwise <code class="docutils literal notranslate"><span class="pre">0</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyObject_GetBuffer">
int <code class="descname">PyObject_GetBuffer</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em>, <a class="reference internal" href="#c.Py_buffer" title="Py_buffer">Py_buffer</a><em> *view</em>, int<em> flags</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_GetBuffer" title="Permalink to this definition">¶</a></dt>
<dd><p>Export <em>obj</em> into a <a class="reference internal" href="#c.Py_buffer" title="Py_buffer"><code class="xref c c-type docutils literal notranslate"><span class="pre">Py_buffer</span></code></a>, <em>view</em>. These arguments must
never be <em>NULL</em>. The <em>flags</em> argument is a bit field indicating what
kind of buffer the caller is prepared to deal with and therefore what
kind of buffer the exporter is allowed to return. The buffer interface
allows for complicated memory sharing possibilities, but some caller may
not be able to handle all the complexity but may want to see if the
exporter will let them take a simpler view to its memory.</p>
<p>Some exporters may not be able to share memory in every possible way and
may need to raise errors to signal to some consumers that something is
just not possible. These errors should be a <a class="reference internal" href="../library/exceptions.html#exceptions.BufferError" title="exceptions.BufferError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BufferError</span></code></a> unless
there is another error that is actually causing the problem. The
exporter can use flags information to simplify how much of the
<a class="reference internal" href="#c.Py_buffer" title="Py_buffer"><code class="xref c c-data docutils literal notranslate"><span class="pre">Py_buffer</span></code></a> structure is filled in with non-default values and/or
raise an error if the object can’t support a simpler view of its memory.</p>
<p><code class="docutils literal notranslate"><span class="pre">0</span></code> is returned on success and <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p>
<p>The following table gives possible values to the <em>flags</em> arguments.</p>
<table class="docutils align-center">
<colgroup>
<col style="width: 38%" />
<col style="width: 62%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Flag</p></th>
<th class="head"><p>Description</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_SIMPLE</span></code></p></td>
<td><p>This is the default flag state. The returned
buffer may or may not have writable memory. The
format of the data will be assumed to be unsigned
bytes. This is a “stand-alone” flag constant. It
never needs to be ‘|’d to the others. The exporter
will raise an error if it cannot provide such a
contiguous buffer of bytes.</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code></p></td>
<td><p>The returned buffer must be writable. If it is
not writable, then raise an error.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_STRIDES</span></code></p></td>
<td><p>This implies <code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_ND</span></code>. The returned
buffer must provide strides information (i.e. the
strides cannot be NULL). This would be used when
the consumer can handle strided, discontiguous
arrays. Handling strides automatically assumes
you can handle shape. The exporter can raise an
error if a strided representation of the data is
not possible (i.e. without the suboffsets).</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_ND</span></code></p></td>
<td><p>The returned buffer must provide shape
information. The memory will be assumed C-style
contiguous (last dimension varies the
fastest). The exporter may raise an error if it
cannot provide this kind of contiguous buffer. If
this is not given then shape will be <em>NULL</em>.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_C_CONTIGUOUS</span></code>
<code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_F_CONTIGUOUS</span></code>
<code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_ANY_CONTIGUOUS</span></code></p></td>
<td><p>These flags indicate that the contiguity returned
buffer must be respectively, C-contiguous (last
dimension varies the fastest), Fortran contiguous
(first dimension varies the fastest) or either
one. All of these flags imply
<code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_STRIDES</span></code> and guarantee that the
strides buffer info structure will be filled in
correctly.</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_INDIRECT</span></code></p></td>
<td><p>This flag indicates the returned buffer must have
suboffsets information (which can be NULL if no
suboffsets are needed). This can be used when
the consumer can handle indirect array
referencing implied by these suboffsets. This
implies <code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_STRIDES</span></code>.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_FORMAT</span></code></p></td>
<td><p>The returned buffer must have true format
information if this flag is provided. This would
be used when the consumer is going to be checking
for what ‘kind’ of data is actually stored. An
exporter should always be able to provide this
information if requested. If format is not
explicitly requested then the format must be
returned as <em>NULL</em> (which means <code class="docutils literal notranslate"><span class="pre">'B'</span></code>, or
unsigned bytes)</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_STRIDED</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_STRIDES</span> <span class="pre">|</span>
<span class="pre">PyBUF_WRITABLE)</span></code>.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_STRIDED_RO</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_STRIDES)</span></code>.</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_RECORDS</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_STRIDES</span> <span class="pre">|</span>
<span class="pre">PyBUF_FORMAT</span> <span class="pre">|</span> <span class="pre">PyBUF_WRITABLE)</span></code>.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_RECORDS_RO</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_STRIDES</span> <span class="pre">|</span>
<span class="pre">PyBUF_FORMAT)</span></code>.</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_FULL</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_INDIRECT</span> <span class="pre">|</span>
<span class="pre">PyBUF_FORMAT</span> <span class="pre">|</span> <span class="pre">PyBUF_WRITABLE)</span></code>.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_FULL_RO</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_INDIRECT</span> <span class="pre">|</span>
<span class="pre">PyBUF_FORMAT)</span></code>.</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_CONTIG</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_ND</span> <span class="pre">|</span>
<span class="pre">PyBUF_WRITABLE)</span></code>.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_CONTIG_RO</span></code></p></td>
<td><p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">(PyBUF_ND)</span></code>.</p></td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_Release">
void <code class="descname">PyBuffer_Release</code><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_buffer" title="Py_buffer">Py_buffer</a><em> *view</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_Release" title="Permalink to this definition">¶</a></dt>
<dd><p>Release the buffer <em>view</em>. This should be called when the buffer
is no longer being used as it may free memory from it.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_SizeFromFormat">
Py_ssize_t <code class="descname">PyBuffer_SizeFromFormat</code><span class="sig-paren">(</span>const char<em> *</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_SizeFromFormat" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the implied <a class="reference internal" href="#c.Py_buffer.itemsize" title="Py_buffer.itemsize"><code class="xref c c-data docutils literal notranslate"><span class="pre">itemsize</span></code></a> from the struct-stype
<code class="xref c c-data docutils literal notranslate"><span class="pre">format</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_IsContiguous">
int <code class="descname">PyBuffer_IsContiguous</code><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_buffer" title="Py_buffer">Py_buffer</a><em> *view</em>, char<em> fortran</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_IsContiguous" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">1</span></code> if the memory defined by the <em>view</em> is C-style (<em>fortran</em> is
<code class="docutils literal notranslate"><span class="pre">'C'</span></code>) or Fortran-style (<em>fortran</em> is <code class="docutils literal notranslate"><span class="pre">'F'</span></code>) contiguous or either one
(<em>fortran</em> is <code class="docutils literal notranslate"><span class="pre">'A'</span></code>). Return <code class="docutils literal notranslate"><span class="pre">0</span></code> otherwise.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_FillContiguousStrides">
void <code class="descname">PyBuffer_FillContiguousStrides</code><span class="sig-paren">(</span>int<em> ndims</em>, Py_ssize_t<em> *shape</em>, Py_ssize_t<em> *strides</em>, int<em> itemsize</em>, char<em> fortran</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_FillContiguousStrides" title="Permalink to this definition">¶</a></dt>
<dd><p>Fill the <em>strides</em> array with byte-strides of a contiguous (C-style if
<em>fortran</em> is <code class="docutils literal notranslate"><span class="pre">'C'</span></code> or Fortran-style if <em>fortran</em> is <code class="docutils literal notranslate"><span class="pre">'F'</span></code>) array of the
given shape with the given number of bytes per element.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_FillInfo">
int <code class="descname">PyBuffer_FillInfo</code><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_buffer" title="Py_buffer">Py_buffer</a><em> *view</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em>, void<em> *buf</em>, Py_ssize_t<em> len</em>, int<em> readonly</em>, int<em> infoflags</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_FillInfo" title="Permalink to this definition">¶</a></dt>
<dd><p>Fill in a buffer-info structure, <em>view</em>, correctly for an exporter that can
only share a contiguous chunk of memory of “unsigned bytes” of the given
length. Return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success and <code class="docutils literal notranslate"><span class="pre">-1</span></code> (with raising an error) on error.</p>
</dd></dl>
</div>
<div class="section" id="memoryview-objects">
<h2>MemoryView objects<a class="headerlink" href="#memoryview-objects" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.</span></p>
</div>
<p>A <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate"><span class="pre">memoryview</span></code></a> object exposes the new C level buffer interface as a
Python object which can then be passed around like any other object.</p>
<dl class="function">
<dt id="c.PyMemoryView_FromObject">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="descname">PyMemoryView_FromObject</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMemoryView_FromObject" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a memoryview object from an object that defines the new buffer
interface.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyMemoryView_FromBuffer">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="descname">PyMemoryView_FromBuffer</code><span class="sig-paren">(</span><a class="reference internal" href="#c.Py_buffer" title="Py_buffer">Py_buffer</a><em> *view</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMemoryView_FromBuffer" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a memoryview object wrapping the given buffer-info structure <em>view</em>.
The memoryview object then owns the buffer, which means you shouldn’t
try to release it yourself: it will be released on deallocation of the
memoryview object.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyMemoryView_GetContiguous">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="descname">PyMemoryView_GetContiguous</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em>, int<em> buffertype</em>, char<em> order</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMemoryView_GetContiguous" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a memoryview object to a contiguous chunk of memory (in either
‘C’ or ‘F’ortran <em>order</em>) from an object that defines the buffer
interface. If memory is contiguous, the memoryview object points to the
original memory. Otherwise copy is made and the memoryview points to a
new bytes object.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyMemoryView_Check">
int <code class="descname">PyMemoryView_Check</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMemoryView_Check" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if the object <em>obj</em> is a memoryview object. It is not
currently allowed to create subclasses of <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate"><span class="pre">memoryview</span></code></a>.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyMemoryView_GET_BUFFER">
<a class="reference internal" href="#c.Py_buffer" title="Py_buffer">Py_buffer</a> *<code class="descname">PyMemoryView_GET_BUFFER</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *obj</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMemoryView_GET_BUFFER" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a pointer to the buffer-info structure wrapped by the given
object. The object <strong>must</strong> be a memoryview instance; this macro doesn’t
check its type, you must do it yourself or you will risk crashes.</p>
</dd></dl>
</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"><span class="std std-ref">Buffer Object Structures</span></a>, under the description for <a class="reference internal" href="typeobj.html#c.PyBufferProcs" title="PyBufferProcs"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyBufferProcs</span></code></a>.</p>
<p>A “buffer object” is defined in the <code class="file docutils literal notranslate"><span class="pre">bufferobject.h</span></code> header (included by
<code class="file docutils literal notranslate"><span class="pre">Python.h</span></code>). 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>
<dl class="type">
<dt id="c.PyBufferObject">
<code class="descname">PyBufferObject</code><a class="headerlink" href="#c.PyBufferObject" title="Permalink to this definition">¶</a></dt>
<dd><p>This subtype of <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> represents a buffer object.</p>
</dd></dl>
<dl class="var">
<dt id="c.PyBuffer_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="descname">PyBuffer_Type</code><a class="headerlink" href="#c.PyBuffer_Type" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-2">The instance of <a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyTypeObject</span></code></a> which represents the Python buffer type;
it is the same object as <code class="docutils literal notranslate"><span class="pre">buffer</span></code> and <code class="docutils literal notranslate"><span class="pre">types.BufferType</span></code> in the Python
layer. .</p>
</dd></dl>
<dl class="var">
<dt id="c.Py_END_OF_BUFFER">
int <code class="descname">Py_END_OF_BUFFER</code><a class="headerlink" href="#c.Py_END_OF_BUFFER" title="Permalink to this definition">¶</a></dt>
<dd><p>This constant may be passed as the <em>size</em> parameter to
<a class="reference internal" href="#c.PyBuffer_FromObject" title="PyBuffer_FromObject"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_FromObject()</span></code></a> or <a class="reference internal" href="#c.PyBuffer_FromReadWriteObject" title="PyBuffer_FromReadWriteObject"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_FromReadWriteObject()</span></code></a>. It
indicates that the new <a class="reference internal" href="#c.PyBufferObject" title="PyBufferObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyBufferObject</span></code></a> should refer to <em>base</em>
object from the specified <em>offset</em> to the end of its exported buffer.
Using this enables the caller to avoid querying the <em>base</em> object for its
length.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_Check">
int <code class="descname">PyBuffer_Check</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *p</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_Check" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if the argument has type <a class="reference internal" href="#c.PyBuffer_Type" title="PyBuffer_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyBuffer_Type</span></code></a>.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_FromObject">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyBuffer_FromObject</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *base</em>, Py_ssize_t<em> offset</em>, Py_ssize_t<em> size</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_FromObject" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a new read-only buffer object. This raises <a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> if
<em>base</em> doesn’t support the read-only buffer protocol or doesn’t provide
exactly one buffer segment, or it raises <a class="reference internal" href="../library/exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> if <em>offset</em> is
less than zero. The buffer will hold a reference to the <em>base</em> object, and
the buffer’s contents will refer to the <em>base</em> object’s buffer interface,
starting as position <em>offset</em> and extending for <em>size</em> bytes. If <em>size</em> is
<code class="xref py py-const docutils literal notranslate"><span class="pre">Py_END_OF_BUFFER</span></code>, then the new buffer’s contents extend to the
length of the <em>base</em> object’s exported buffer data.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.5: </span>This function used an <code class="xref c c-type docutils literal notranslate"><span class="pre">int</span></code> type for <em>offset</em> and <em>size</em>. This
might require changes in your code for properly supporting 64-bit
systems.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_FromReadWriteObject">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyBuffer_FromReadWriteObject</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *base</em>, Py_ssize_t<em> offset</em>, Py_ssize_t<em> size</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_FromReadWriteObject" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a new writable buffer object. Parameters and exceptions are similar
to those for <a class="reference internal" href="#c.PyBuffer_FromObject" title="PyBuffer_FromObject"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_FromObject()</span></code></a>. If the <em>base</em> object does not
export the writeable buffer protocol, then <a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> is raised.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.5: </span>This function used an <code class="xref c c-type docutils literal notranslate"><span class="pre">int</span></code> type for <em>offset</em> and <em>size</em>. This
might require changes in your code for properly supporting 64-bit
systems.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_FromMemory">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyBuffer_FromMemory</code><span class="sig-paren">(</span>void<em> *ptr</em>, Py_ssize_t<em> size</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_FromMemory" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a new read-only buffer object that reads from a specified location
in memory, with a specified size. The caller is responsible for ensuring
that the memory buffer, passed in as <em>ptr</em>, is not deallocated while the
returned buffer object exists. Raises <a class="reference internal" href="../library/exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> if <em>size</em> is less
than zero. Note that <code class="xref py py-const docutils literal notranslate"><span class="pre">Py_END_OF_BUFFER</span></code> may <em>not</em> be passed for the
<em>size</em> parameter; <a class="reference internal" href="../library/exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> will be raised in that case.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.5: </span>This function used an <code class="xref c c-type docutils literal notranslate"><span class="pre">int</span></code> type for <em>size</em>. This might require
changes in your code for properly supporting 64-bit systems.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_FromReadWriteMemory">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyBuffer_FromReadWriteMemory</code><span class="sig-paren">(</span>void<em> *ptr</em>, Py_ssize_t<em> size</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_FromReadWriteMemory" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Similar to <a class="reference internal" href="#c.PyBuffer_FromMemory" title="PyBuffer_FromMemory"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_FromMemory()</span></code></a>, but the returned buffer is
writable.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.5: </span>This function used an <code class="xref c c-type docutils literal notranslate"><span class="pre">int</span></code> type for <em>size</em>. This might require
changes in your code for properly supporting 64-bit systems.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="c.PyBuffer_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyBuffer_New</code><span class="sig-paren">(</span>Py_ssize_t<em> size</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_New" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a new writable buffer object that maintains its own memory buffer of
<em>size</em> bytes. <a class="reference internal" href="../library/exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> is returned if <em>size</em> is not zero or
positive. Note that the memory buffer (as returned by
<a class="reference internal" href="objbuffer.html#c.PyObject_AsWriteBuffer" title="PyObject_AsWriteBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_AsWriteBuffer()</span></code></a>) is not specifically aligned.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.5: </span>This function used an <code class="xref c c-type docutils literal notranslate"><span class="pre">int</span></code> type for <em>size</em>. This might require
changes in your code for properly supporting 64-bit systems.</p>
</div>
</dd></dl>
</div>
</div>
</div>
</div>
</div>
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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>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="unicode.html"
title="previous chapter">Unicode Objects and Codecs</a></p>
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title="next chapter">Tuple Objects</a></p>
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