<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /> <title>Buffer Protocol — Python 3.7.4 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.7.4 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="Old Buffer Protocol" href="objbuffer.html" /> <link rel="prev" title="Iterator Protocol" href="iter.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/c-api/buffer.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> <script type="text/javascript" src="../_static/switchers.js"></script> <style> @media only screen { table.full-width-table { width: 100%; } } </style> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="objbuffer.html" title="Old Buffer Protocol" accesskey="N">next</a> |</li> <li class="right" > <a href="iter.html" title="Iterator Protocol" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <span class="language_switcher_placeholder">en</span> <span class="version_switcher_placeholder">3.7.4</span> <a href="../index.html">Documentation </a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li> <li class="nav-item nav-item-2"><a href="abstract.html" accesskey="U">Abstract Objects Layer</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="buffer-protocol"> <span id="bufferobjects"></span><span id="index-0"></span><h1>Buffer Protocol<a class="headerlink" href="#buffer-protocol" title="Permalink to this headline">¶</a></h1> <p>Certain objects available in Python wrap access to an underlying memory array or <em>buffer</em>. Such objects include the built-in <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> and <a class="reference internal" href="../library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a>, and some extension types like <a class="reference internal" href="../library/array.html#array.array" title="array.array"><code class="xref py py-class docutils literal notranslate"><span class="pre">array.array</span></code></a>. Third-party libraries may define their own types for special purposes, such as image processing or numeric analysis.</p> <p>While each of these types have their own semantics, they share the common characteristic of being backed by a possibly large memory buffer. It is then desirable, in some situations, to access that buffer directly and without intermediate copying.</p> <p>Python provides such a facility at the C level in the form of the <a class="reference internal" href="#bufferobjects"><span class="std std-ref">buffer protocol</span></a>. This protocol has two sides:</p> <ul class="simple" id="index-1"> <li><p>on the producer side, a type can export a “buffer interface” which allows objects of that type to expose information about their underlying buffer. This interface is described in the section <a class="reference internal" href="typeobj.html#buffer-structs"><span class="std std-ref">Buffer Object Structures</span></a>;</p></li> <li><p>on the consumer side, several means are available to obtain a pointer to the raw underlying data of an object (for example a method parameter).</p></li> </ul> <p>Simple objects such as <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> and <a class="reference internal" href="../library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a> expose their underlying buffer in byte-oriented form. Other forms are possible; for example, the elements exposed by an <a class="reference internal" href="../library/array.html#array.array" title="array.array"><code class="xref py py-class docutils literal notranslate"><span class="pre">array.array</span></code></a> can be multi-byte values.</p> <p>An example consumer of the buffer interface is the <a class="reference internal" href="../library/io.html#io.BufferedIOBase.write" title="io.BufferedIOBase.write"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code></a> method of file objects: any object that can export a series of bytes through the buffer interface can be written to a file. While <code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code> only needs read-only access to the internal contents of the object passed to it, other methods such as <a class="reference internal" href="../library/io.html#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><code class="xref py py-meth docutils literal notranslate"><span class="pre">readinto()</span></code></a> need write access to the contents of their argument. The buffer interface allows objects to selectively allow or reject exporting of read-write and read-only buffers.</p> <p>There are two ways for a consumer of the buffer interface to acquire a buffer over a target object:</p> <ul class="simple"> <li><p>call <a class="reference internal" href="#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a> with the right parameters;</p></li> <li><p>call <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> (or one of its siblings) with one of the <code class="docutils literal notranslate"><span class="pre">y*</span></code>, <code class="docutils literal notranslate"><span class="pre">w*</span></code> or <code class="docutils literal notranslate"><span class="pre">s*</span></code> <a class="reference internal" href="arg.html#arg-parsing"><span class="std std-ref">format codes</span></a>.</p></li> </ul> <p>In both cases, <a class="reference internal" href="#c.PyBuffer_Release" title="PyBuffer_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_Release()</span></code></a> must be called when the buffer isn’t needed anymore. Failure to do so could lead to various issues such as resource leaks.</p> <div class="section" id="buffer-structure"> <span id="id1"></span><h2>Buffer structure<a class="headerlink" href="#buffer-structure" title="Permalink to this headline">¶</a></h2> <p>Buffer structures (or simply “buffers”) are useful as a way to expose the binary data from another object 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> <p>Contrary to most data types exposed by the Python interpreter, buffers are not <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> pointers but rather simple C structures. This allows them to be created and copied very simply. When a generic wrapper around a buffer is needed, a <a class="reference internal" href="memoryview.html#memoryview-objects"><span class="std std-ref">memoryview</span></a> object can be created.</p> <p>For short instructions how to write an exporting object, see <a class="reference internal" href="typeobj.html#buffer-structs"><span class="std std-ref">Buffer Object Structures</span></a>. For obtaining a buffer, see <a class="reference internal" href="#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a>.</p> <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 logical structure described by the buffer fields. This can be any location within the underlying physical memory block of the exporter. For example, with negative <a class="reference internal" href="#c.Py_buffer.strides" title="Py_buffer.strides"><code class="xref c c-member docutils literal notranslate"><span class="pre">strides</span></code></a> the value may point to the end of the memory block.</p> <p>For <a class="reference internal" href="../glossary.html#term-contiguous"><span class="xref std std-term">contiguous</span></a> arrays, the value points to the beginning of the memory block.</p> </dd></dl> <dl class="member"> <dt id="c.Py_buffer.obj"> void *<code class="descname">obj</code><a class="headerlink" href="#c.Py_buffer.obj" title="Permalink to this definition">¶</a></dt> <dd><p>A new reference to the exporting object. The reference is owned by the consumer and automatically decremented and set to <em>NULL</em> by <a class="reference internal" href="#c.PyBuffer_Release" title="PyBuffer_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_Release()</span></code></a>. The field is the equivalent of the return value of any standard C-API function.</p> <p>As a special case, for <em>temporary</em> buffers that are wrapped by <a class="reference internal" href="memoryview.html#c.PyMemoryView_FromBuffer" title="PyMemoryView_FromBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMemoryView_FromBuffer()</span></code></a> or <a class="reference internal" href="#c.PyBuffer_FillInfo" title="PyBuffer_FillInfo"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_FillInfo()</span></code></a> this field is <em>NULL</em>. In general, exporting objects MUST NOT use this scheme.</p> </dd></dl> <dl class="member"> <dt id="c.Py_buffer.len"> Py_ssize_t <code class="descname">len</code><a class="headerlink" href="#c.Py_buffer.len" title="Permalink to this definition">¶</a></dt> <dd><p><code class="docutils literal notranslate"><span class="pre">product(shape)</span> <span class="pre">*</span> <span class="pre">itemsize</span></code>. For contiguous arrays, this is the length of the underlying memory block. For non-contiguous arrays, it is the length that the logical structure would have if it were copied to a contiguous representation.</p> <p>Accessing <code class="docutils literal notranslate"><span class="pre">((char</span> <span class="pre">*)buf)[0]</span> <span class="pre">up</span> <span class="pre">to</span> <span class="pre">((char</span> <span class="pre">*)buf)[len-1]</span></code> is only valid if the buffer has been obtained by a request that guarantees contiguity. In most cases such a request will be <a class="reference internal" href="#c.PyBUF_SIMPLE" title="PyBUF_SIMPLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_SIMPLE</span></code></a> or <a class="reference internal" href="#c.PyBUF_WRITABLE" title="PyBUF_WRITABLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code></a>.</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. This field is controlled by the <a class="reference internal" href="#c.PyBUF_WRITABLE" title="PyBUF_WRITABLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code></a> flag.</p> </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>Item size in bytes of a single element. Same as the value of <a class="reference internal" href="../library/struct.html#struct.calcsize" title="struct.calcsize"><code class="xref py py-func docutils literal notranslate"><span class="pre">struct.calcsize()</span></code></a> called on non-NULL <a class="reference internal" href="#c.Py_buffer.format" title="Py_buffer.format"><code class="xref c c-member docutils literal notranslate"><span class="pre">format</span></code></a> values.</p> <p>Important exception: If a consumer requests a buffer without the <a class="reference internal" href="#c.PyBUF_FORMAT" title="PyBUF_FORMAT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_FORMAT</span></code></a> flag, <a class="reference internal" href="#c.Py_buffer.format" title="Py_buffer.format"><code class="xref c c-member docutils literal notranslate"><span class="pre">format</span></code></a> will be set to <em>NULL</em>, but <a class="reference internal" href="#c.Py_buffer.itemsize" title="Py_buffer.itemsize"><code class="xref c c-member docutils literal notranslate"><span class="pre">itemsize</span></code></a> still has the value for the original format.</p> <p>If <a class="reference internal" href="#c.Py_buffer.shape" title="Py_buffer.shape"><code class="xref c c-member docutils literal notranslate"><span class="pre">shape</span></code></a> is present, the equality <code class="docutils literal notranslate"><span class="pre">product(shape)</span> <span class="pre">*</span> <span class="pre">itemsize</span> <span class="pre">==</span> <span class="pre">len</span></code> still holds and the consumer can use <a class="reference internal" href="#c.Py_buffer.itemsize" title="Py_buffer.itemsize"><code class="xref c c-member docutils literal notranslate"><span class="pre">itemsize</span></code></a> to navigate the buffer.</p> <p>If <a class="reference internal" href="#c.Py_buffer.shape" title="Py_buffer.shape"><code class="xref c c-member docutils literal notranslate"><span class="pre">shape</span></code></a> is <em>NULL</em> as a result of a <a class="reference internal" href="#c.PyBUF_SIMPLE" title="PyBUF_SIMPLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_SIMPLE</span></code></a> or a <a class="reference internal" href="#c.PyBUF_WRITABLE" title="PyBUF_WRITABLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code></a> request, the consumer must disregard <a class="reference internal" href="#c.Py_buffer.itemsize" title="Py_buffer.itemsize"><code class="xref c c-member docutils literal notranslate"><span class="pre">itemsize</span></code></a> and assume <code class="docutils literal notranslate"><span class="pre">itemsize</span> <span class="pre">==</span> <span class="pre">1</span></code>.</p> </dd></dl> <dl class="member"> <dt id="c.Py_buffer.format"> const char *<code class="descname">format</code><a class="headerlink" href="#c.Py_buffer.format" title="Permalink to this definition">¶</a></dt> <dd><p>A <em>NUL</em> terminated string in <a class="reference internal" href="../library/struct.html#module-struct" title="struct: Interpret bytes as packed binary data."><code class="xref py py-mod docutils literal notranslate"><span class="pre">struct</span></code></a> module style syntax describing the contents of a single item. If this is <em>NULL</em>, <code class="docutils literal notranslate"><span class="pre">"B"</span></code> (unsigned bytes) is assumed.</p> <p>This field is controlled by the <a class="reference internal" href="#c.PyBUF_FORMAT" title="PyBUF_FORMAT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_FORMAT</span></code></a> flag.</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 an n-dimensional array. If it is <code class="docutils literal notranslate"><span class="pre">0</span></code>, <a class="reference internal" href="#c.Py_buffer.buf" title="Py_buffer.buf"><code class="xref c c-member docutils literal notranslate"><span class="pre">buf</span></code></a> points to a single item representing a scalar. In this case, <a class="reference internal" href="#c.Py_buffer.shape" title="Py_buffer.shape"><code class="xref c c-member docutils literal notranslate"><span class="pre">shape</span></code></a>, <a class="reference internal" href="#c.Py_buffer.strides" title="Py_buffer.strides"><code class="xref c c-member docutils literal notranslate"><span class="pre">strides</span></code></a> and <a class="reference internal" href="#c.Py_buffer.suboffsets" title="Py_buffer.suboffsets"><code class="xref c c-member docutils literal notranslate"><span class="pre">suboffsets</span></code></a> MUST be <em>NULL</em>.</p> <p>The macro <code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_MAX_NDIM</span></code> limits the maximum number of dimensions to 64. Exporters MUST respect this limit, consumers of multi-dimensional buffers SHOULD be able to handle up to <code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_MAX_NDIM</span></code> dimensions.</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> of length <a class="reference internal" href="#c.Py_buffer.ndim" title="Py_buffer.ndim"><code class="xref c c-member docutils literal notranslate"><span class="pre">ndim</span></code></a> indicating the shape of the memory as an n-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[ndim-1]</span> <span class="pre">*</span> <span class="pre">itemsize</span></code> MUST be equal to <a class="reference internal" href="#c.Py_buffer.len" title="Py_buffer.len"><code class="xref c c-member docutils literal notranslate"><span class="pre">len</span></code></a>.</p> <p>Shape values are restricted to <code class="docutils literal notranslate"><span class="pre">shape[n]</span> <span class="pre">>=</span> <span class="pre">0</span></code>. The case <code class="docutils literal notranslate"><span class="pre">shape[n]</span> <span class="pre">==</span> <span class="pre">0</span></code> requires special attention. See <a class="reference internal" href="#complex-arrays">complex arrays</a> for further information.</p> <p>The shape array is read-only for the consumer.</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> of length <a class="reference internal" href="#c.Py_buffer.ndim" title="Py_buffer.ndim"><code class="xref c c-member docutils literal notranslate"><span class="pre">ndim</span></code></a> giving the number of bytes to skip to get to a new element in each dimension.</p> <p>Stride values can be any integer. For regular arrays, strides are usually positive, but a consumer MUST be able to handle the case <code class="docutils literal notranslate"><span class="pre">strides[n]</span> <span class="pre"><=</span> <span class="pre">0</span></code>. See <a class="reference internal" href="#complex-arrays">complex arrays</a> for further information.</p> <p>The strides array is read-only for the consumer.</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> of length <a class="reference internal" href="#c.Py_buffer.ndim" title="Py_buffer.ndim"><code class="xref c c-member docutils literal notranslate"><span class="pre">ndim</span></code></a>. If <code class="docutils literal notranslate"><span class="pre">suboffsets[n]</span> <span class="pre">>=</span> <span class="pre">0</span></code>, the values stored along the nth dimension are pointers and the suboffset value dictates how many bytes to add to each pointer after de-referencing. A suboffset value that is 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>This type of array representation is used by the Python Imaging Library (PIL). See <a class="reference internal" href="#complex-arrays">complex arrays</a> for further information how to access elements of such an array.</p> <p>The suboffsets array is read-only for the consumer.</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 MUST NOT alter this value.</p> </dd></dl> </dd></dl> </div> <div class="section" id="buffer-request-types"> <span id="id2"></span><h2>Buffer request types<a class="headerlink" href="#buffer-request-types" title="Permalink to this headline">¶</a></h2> <p>Buffers are usually obtained by sending a buffer request to an exporting object via <a class="reference internal" href="#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a>. Since the complexity of the logical structure of the memory can vary drastically, the consumer uses the <em>flags</em> argument to specify the exact buffer type it can handle.</p> <p>All <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> fields are unambiguously defined by the request type.</p> <div class="section" id="request-independent-fields"> <h3>request-independent fields<a class="headerlink" href="#request-independent-fields" title="Permalink to this headline">¶</a></h3> <p>The following fields are not influenced by <em>flags</em> and must always be filled in with the correct values: <a class="reference internal" href="#c.Py_buffer.obj" title="Py_buffer.obj"><code class="xref c c-member docutils literal notranslate"><span class="pre">obj</span></code></a>, <a class="reference internal" href="#c.Py_buffer.buf" title="Py_buffer.buf"><code class="xref c c-member docutils literal notranslate"><span class="pre">buf</span></code></a>, <a class="reference internal" href="#c.Py_buffer.len" title="Py_buffer.len"><code class="xref c c-member docutils literal notranslate"><span class="pre">len</span></code></a>, <a class="reference internal" href="#c.Py_buffer.itemsize" title="Py_buffer.itemsize"><code class="xref c c-member docutils literal notranslate"><span class="pre">itemsize</span></code></a>, <a class="reference internal" href="#c.Py_buffer.ndim" title="Py_buffer.ndim"><code class="xref c c-member docutils literal notranslate"><span class="pre">ndim</span></code></a>.</p> </div> <div class="section" id="readonly-format"> <h3>readonly, format<a class="headerlink" href="#readonly-format" title="Permalink to this headline">¶</a></h3> <blockquote> <div><dl class="macro"> <dt id="c.PyBUF_WRITABLE"> <code class="descname">PyBUF_WRITABLE</code><a class="headerlink" href="#c.PyBUF_WRITABLE" title="Permalink to this definition">¶</a></dt> <dd><p>Controls the <a class="reference internal" href="#c.Py_buffer.readonly" title="Py_buffer.readonly"><code class="xref c c-member docutils literal notranslate"><span class="pre">readonly</span></code></a> field. If set, the exporter MUST provide a writable buffer or else report failure. Otherwise, the exporter MAY provide either a read-only or writable buffer, but the choice MUST be consistent for all consumers.</p> </dd></dl> <dl class="macro"> <dt id="c.PyBUF_FORMAT"> <code class="descname">PyBUF_FORMAT</code><a class="headerlink" href="#c.PyBUF_FORMAT" title="Permalink to this definition">¶</a></dt> <dd><p>Controls the <a class="reference internal" href="#c.Py_buffer.format" title="Py_buffer.format"><code class="xref c c-member docutils literal notranslate"><span class="pre">format</span></code></a> field. If set, this field MUST be filled in correctly. Otherwise, this field MUST be <em>NULL</em>.</p> </dd></dl> </div></blockquote> <p><a class="reference internal" href="#c.PyBUF_WRITABLE" title="PyBUF_WRITABLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code></a> can be |’d to any of the flags in the next section. Since <a class="reference internal" href="#c.PyBUF_SIMPLE" title="PyBUF_SIMPLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_SIMPLE</span></code></a> is defined as 0, <a class="reference internal" href="#c.PyBUF_WRITABLE" title="PyBUF_WRITABLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code></a> can be used as a stand-alone flag to request a simple writable buffer.</p> <p><a class="reference internal" href="#c.PyBUF_FORMAT" title="PyBUF_FORMAT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_FORMAT</span></code></a> can be |’d to any of the flags except <a class="reference internal" href="#c.PyBUF_SIMPLE" title="PyBUF_SIMPLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_SIMPLE</span></code></a>. The latter already implies format <code class="docutils literal notranslate"><span class="pre">B</span></code> (unsigned bytes).</p> </div> <div class="section" id="shape-strides-suboffsets"> <h3>shape, strides, suboffsets<a class="headerlink" href="#shape-strides-suboffsets" title="Permalink to this headline">¶</a></h3> <p>The flags that control the logical structure of the memory are listed in decreasing order of complexity. Note that each flag contains all bits of the flags below it.</p> <table class="docutils align-center"> <colgroup> <col style="width: 51%" /> <col style="width: 12%" /> <col style="width: 16%" /> <col style="width: 21%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Request</p></th> <th class="head"><p>shape</p></th> <th class="head"><p>strides</p></th> <th class="head"><p>suboffsets</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_INDIRECT"> <code class="descname">PyBUF_INDIRECT</code><a class="headerlink" href="#c.PyBUF_INDIRECT" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>if needed</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt id="c.PyBUF_STRIDES"> <code class="descname">PyBUF_STRIDES</code><a class="headerlink" href="#c.PyBUF_STRIDES" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> </tr> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_ND"> <code class="descname">PyBUF_ND</code><a class="headerlink" href="#c.PyBUF_ND" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>NULL</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt id="c.PyBUF_SIMPLE"> <code class="descname">PyBUF_SIMPLE</code><a class="headerlink" href="#c.PyBUF_SIMPLE" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>NULL</p></td> <td><p>NULL</p></td> <td><p>NULL</p></td> </tr> </tbody> </table> </div> <div class="section" id="contiguity-requests"> <span id="index-2"></span><h3>contiguity requests<a class="headerlink" href="#contiguity-requests" title="Permalink to this headline">¶</a></h3> <p>C or Fortran <a class="reference internal" href="../glossary.html#term-contiguous"><span class="xref std std-term">contiguity</span></a> can be explicitly requested, with and without stride information. Without stride information, the buffer must be C-contiguous.</p> <table class="docutils align-center"> <colgroup> <col style="width: 49%" /> <col style="width: 10%" /> <col style="width: 13%" /> <col style="width: 17%" /> <col style="width: 11%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Request</p></th> <th class="head"><p>shape</p></th> <th class="head"><p>strides</p></th> <th class="head"><p>suboffsets</p></th> <th class="head"><p>contig</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_C_CONTIGUOUS"> <code class="descname">PyBUF_C_CONTIGUOUS</code><a class="headerlink" href="#c.PyBUF_C_CONTIGUOUS" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>C</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt id="c.PyBUF_F_CONTIGUOUS"> <code class="descname">PyBUF_F_CONTIGUOUS</code><a class="headerlink" href="#c.PyBUF_F_CONTIGUOUS" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>F</p></td> </tr> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_ANY_CONTIGUOUS"> <code class="descname">PyBUF_ANY_CONTIGUOUS</code><a class="headerlink" href="#c.PyBUF_ANY_CONTIGUOUS" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>C or F</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt> <code class="descname">PyBUF_ND</code></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>NULL</p></td> <td><p>C</p></td> </tr> </tbody> </table> </div> <div class="section" id="compound-requests"> <h3>compound requests<a class="headerlink" href="#compound-requests" title="Permalink to this headline">¶</a></h3> <p>All possible requests are fully defined by some combination of the flags in the previous section. For convenience, the buffer protocol provides frequently used combinations as single flags.</p> <p>In the following table <em>U</em> stands for undefined contiguity. The consumer would have to call <a class="reference internal" href="#c.PyBuffer_IsContiguous" title="PyBuffer_IsContiguous"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_IsContiguous()</span></code></a> to determine contiguity.</p> <table class="docutils align-center"> <colgroup> <col style="width: 36%" /> <col style="width: 8%" /> <col style="width: 11%" /> <col style="width: 14%" /> <col style="width: 9%" /> <col style="width: 12%" /> <col style="width: 9%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Request</p></th> <th class="head"><p>shape</p></th> <th class="head"><p>strides</p></th> <th class="head"><p>suboffsets</p></th> <th class="head"><p>contig</p></th> <th class="head"><p>readonly</p></th> <th class="head"><p>format</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_FULL"> <code class="descname">PyBUF_FULL</code><a class="headerlink" href="#c.PyBUF_FULL" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>if needed</p></td> <td><p>U</p></td> <td><p>0</p></td> <td><p>yes</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt id="c.PyBUF_FULL_RO"> <code class="descname">PyBUF_FULL_RO</code><a class="headerlink" href="#c.PyBUF_FULL_RO" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>if needed</p></td> <td><p>U</p></td> <td><p>1 or 0</p></td> <td><p>yes</p></td> </tr> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_RECORDS"> <code class="descname">PyBUF_RECORDS</code><a class="headerlink" href="#c.PyBUF_RECORDS" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>U</p></td> <td><p>0</p></td> <td><p>yes</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt id="c.PyBUF_RECORDS_RO"> <code class="descname">PyBUF_RECORDS_RO</code><a class="headerlink" href="#c.PyBUF_RECORDS_RO" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>U</p></td> <td><p>1 or 0</p></td> <td><p>yes</p></td> </tr> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_STRIDED"> <code class="descname">PyBUF_STRIDED</code><a class="headerlink" href="#c.PyBUF_STRIDED" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>U</p></td> <td><p>0</p></td> <td><p>NULL</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt id="c.PyBUF_STRIDED_RO"> <code class="descname">PyBUF_STRIDED_RO</code><a class="headerlink" href="#c.PyBUF_STRIDED_RO" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>U</p></td> <td><p>1 or 0</p></td> <td><p>NULL</p></td> </tr> <tr class="row-even"><td><dl class="macro"> <dt id="c.PyBUF_CONTIG"> <code class="descname">PyBUF_CONTIG</code><a class="headerlink" href="#c.PyBUF_CONTIG" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>NULL</p></td> <td><p>C</p></td> <td><p>0</p></td> <td><p>NULL</p></td> </tr> <tr class="row-odd"><td><dl class="macro"> <dt id="c.PyBUF_CONTIG_RO"> <code class="descname">PyBUF_CONTIG_RO</code><a class="headerlink" href="#c.PyBUF_CONTIG_RO" title="Permalink to this definition">¶</a></dt> <dd></dd></dl> </td> <td><p>yes</p></td> <td><p>NULL</p></td> <td><p>NULL</p></td> <td><p>C</p></td> <td><p>1 or 0</p></td> <td><p>NULL</p></td> </tr> </tbody> </table> </div> </div> <div class="section" id="complex-arrays"> <h2>Complex arrays<a class="headerlink" href="#complex-arrays" title="Permalink to this headline">¶</a></h2> <div class="section" id="numpy-style-shape-and-strides"> <h3>NumPy-style: shape and strides<a class="headerlink" href="#numpy-style-shape-and-strides" title="Permalink to this headline">¶</a></h3> <p>The logical structure of NumPy-style arrays is defined by <a class="reference internal" href="#c.Py_buffer.itemsize" title="Py_buffer.itemsize"><code class="xref c c-member docutils literal notranslate"><span class="pre">itemsize</span></code></a>, <a class="reference internal" href="#c.Py_buffer.ndim" title="Py_buffer.ndim"><code class="xref c c-member docutils literal notranslate"><span class="pre">ndim</span></code></a>, <a class="reference internal" href="#c.Py_buffer.shape" title="Py_buffer.shape"><code class="xref c c-member docutils literal notranslate"><span class="pre">shape</span></code></a> and <a class="reference internal" href="#c.Py_buffer.strides" title="Py_buffer.strides"><code class="xref c c-member docutils literal notranslate"><span class="pre">strides</span></code></a>.</p> <p>If <code class="docutils literal notranslate"><span class="pre">ndim</span> <span class="pre">==</span> <span class="pre">0</span></code>, the memory location pointed to by <a class="reference internal" href="#c.Py_buffer.buf" title="Py_buffer.buf"><code class="xref c c-member docutils literal notranslate"><span class="pre">buf</span></code></a> is interpreted as a scalar of size <a class="reference internal" href="#c.Py_buffer.itemsize" title="Py_buffer.itemsize"><code class="xref c c-member docutils literal notranslate"><span class="pre">itemsize</span></code></a>. In that case, both <a class="reference internal" href="#c.Py_buffer.shape" title="Py_buffer.shape"><code class="xref c c-member docutils literal notranslate"><span class="pre">shape</span></code></a> and <a class="reference internal" href="#c.Py_buffer.strides" title="Py_buffer.strides"><code class="xref c c-member docutils literal notranslate"><span class="pre">strides</span></code></a> are <em>NULL</em>.</p> <p>If <a class="reference internal" href="#c.Py_buffer.strides" title="Py_buffer.strides"><code class="xref c c-member docutils literal notranslate"><span class="pre">strides</span></code></a> is <em>NULL</em>, the array is interpreted as a standard n-dimensional C-array. Otherwise, the consumer must access an n-dimensional array as follows:</p> <blockquote> <div><p><code class="docutils literal notranslate"><span class="pre">ptr</span> <span class="pre">=</span> <span class="pre">(char</span> <span class="pre">*)buf</span> <span class="pre">+</span> <span class="pre">indices[0]</span> <span class="pre">*</span> <span class="pre">strides[0]</span> <span class="pre">+</span> <span class="pre">...</span> <span class="pre">+</span> <span class="pre">indices[n-1]</span> <span class="pre">*</span> <span class="pre">strides[n-1]</span></code> <code class="docutils literal notranslate"><span class="pre">item</span> <span class="pre">=</span> <span class="pre">*((typeof(item)</span> <span class="pre">*)ptr);</span></code></p> </div></blockquote> <p>As noted above, <a class="reference internal" href="#c.Py_buffer.buf" title="Py_buffer.buf"><code class="xref c c-member docutils literal notranslate"><span class="pre">buf</span></code></a> can point to any location within the actual memory block. An exporter can check the validity of a buffer with this function:</p> <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">verify_structure</span><span class="p">(</span><span class="n">memlen</span><span class="p">,</span> <span class="n">itemsize</span><span class="p">,</span> <span class="n">ndim</span><span class="p">,</span> <span class="n">shape</span><span class="p">,</span> <span class="n">strides</span><span class="p">,</span> <span class="n">offset</span><span class="p">):</span> <span class="sd">"""Verify that the parameters represent a valid array within</span> <span class="sd"> the bounds of the allocated memory:</span> <span class="sd"> char *mem: start of the physical memory block</span> <span class="sd"> memlen: length of the physical memory block</span> <span class="sd"> offset: (char *)buf - mem</span> <span class="sd"> """</span> <span class="k">if</span> <span class="n">offset</span> <span class="o">%</span> <span class="n">itemsize</span><span class="p">:</span> <span class="k">return</span> <span class="bp">False</span> <span class="k">if</span> <span class="n">offset</span> <span class="o"><</span> <span class="mi">0</span> <span class="ow">or</span> <span class="n">offset</span><span class="o">+</span><span class="n">itemsize</span> <span class="o">></span> <span class="n">memlen</span><span class="p">:</span> <span class="k">return</span> <span class="bp">False</span> <span class="k">if</span> <span class="nb">any</span><span class="p">(</span><span class="n">v</span> <span class="o">%</span> <span class="n">itemsize</span> <span class="k">for</span> <span class="n">v</span> <span class="ow">in</span> <span class="n">strides</span><span class="p">):</span> <span class="k">return</span> <span class="bp">False</span> <span class="k">if</span> <span class="n">ndim</span> <span class="o"><=</span> <span class="mi">0</span><span class="p">:</span> <span class="k">return</span> <span class="n">ndim</span> <span class="o">==</span> <span class="mi">0</span> <span class="ow">and</span> <span class="ow">not</span> <span class="n">shape</span> <span class="ow">and</span> <span class="ow">not</span> <span class="n">strides</span> <span class="k">if</span> <span class="mi">0</span> <span class="ow">in</span> <span class="n">shape</span><span class="p">:</span> <span class="k">return</span> <span class="bp">True</span> <span class="n">imin</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span><span class="n">strides</span><span class="p">[</span><span class="n">j</span><span class="p">]</span><span class="o">*</span><span class="p">(</span><span class="n">shape</span><span class="p">[</span><span class="n">j</span><span class="p">]</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span> <span class="k">for</span> <span class="n">j</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">ndim</span><span class="p">)</span> <span class="k">if</span> <span class="n">strides</span><span class="p">[</span><span class="n">j</span><span class="p">]</span> <span class="o"><=</span> <span class="mi">0</span><span class="p">)</span> <span class="n">imax</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span><span class="n">strides</span><span class="p">[</span><span class="n">j</span><span class="p">]</span><span class="o">*</span><span class="p">(</span><span class="n">shape</span><span class="p">[</span><span class="n">j</span><span class="p">]</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span> <span class="k">for</span> <span class="n">j</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">ndim</span><span class="p">)</span> <span class="k">if</span> <span class="n">strides</span><span class="p">[</span><span class="n">j</span><span class="p">]</span> <span class="o">></span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span> <span class="o"><=</span> <span class="n">offset</span><span class="o">+</span><span class="n">imin</span> <span class="ow">and</span> <span class="n">offset</span><span class="o">+</span><span class="n">imax</span><span class="o">+</span><span class="n">itemsize</span> <span class="o"><=</span> <span class="n">memlen</span> </pre></div> </div> </div> <div class="section" id="pil-style-shape-strides-and-suboffsets"> <h3>PIL-style: shape, strides and suboffsets<a class="headerlink" href="#pil-style-shape-strides-and-suboffsets" title="Permalink to this headline">¶</a></h3> <p>In addition to the regular items, PIL-style arrays can contain pointers that must be followed in order to get to the next element in a dimension. For example, the regular three-dimensional C-array <code class="docutils literal notranslate"><span class="pre">char</span> <span class="pre">v[2][2][3]</span></code> can also be viewed as an array of 2 pointers to 2 two-dimensional arrays: <code class="docutils literal notranslate"><span class="pre">char</span> <span class="pre">(*v[2])[2][3]</span></code>. In suboffsets representation, those two pointers can be embedded at the start of <a class="reference internal" href="#c.Py_buffer.buf" title="Py_buffer.buf"><code class="xref c c-member docutils literal notranslate"><span class="pre">buf</span></code></a>, pointing to two <code class="docutils literal notranslate"><span class="pre">char</span> <span class="pre">x[2][3]</span></code> arrays that can be located anywhere in memory.</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> </div> </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>. When <code class="docutils literal notranslate"><span class="pre">1</span></code> is returned, it doesn’t guarantee that <a class="reference internal" href="#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a> will succeed. This function always succeeds.</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> *exporter</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>Send a request to <em>exporter</em> to fill in <em>view</em> as specified by <em>flags</em>. If the exporter cannot provide a buffer of the exact type, it MUST raise <code class="xref c c-data docutils literal notranslate"><span class="pre">PyExc_BufferError</span></code>, set <code class="xref c c-member docutils literal notranslate"><span class="pre">view->obj</span></code> to <em>NULL</em> and return <code class="docutils literal notranslate"><span class="pre">-1</span></code>.</p> <p>On success, fill in <em>view</em>, set <code class="xref c c-member docutils literal notranslate"><span class="pre">view->obj</span></code> to a new reference to <em>exporter</em> and return 0. In the case of chained buffer providers that redirect requests to a single object, <code class="xref c c-member docutils literal notranslate"><span class="pre">view->obj</span></code> MAY refer to this object instead of <em>exporter</em> (See <a class="reference internal" href="typeobj.html#buffer-structs"><span class="std std-ref">Buffer Object Structures</span></a>).</p> <p>Successful calls to <a class="reference internal" href="#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a> must be paired with calls to <a class="reference internal" href="#c.PyBuffer_Release" title="PyBuffer_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_Release()</span></code></a>, similar to <code class="xref c c-func docutils literal notranslate"><span class="pre">malloc()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">free()</span></code>. Thus, after the consumer is done with the buffer, <a class="reference internal" href="#c.PyBuffer_Release" title="PyBuffer_Release"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyBuffer_Release()</span></code></a> must be called exactly once.</p> </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> and decrement the reference count for <code class="xref c c-member docutils literal notranslate"><span class="pre">view->obj</span></code>. This function MUST be called when the buffer is no longer being used, otherwise reference leaks may occur.</p> <p>It is an error to call this function on a buffer that was not obtained via <a class="reference internal" href="#c.PyObject_GetBuffer" title="PyObject_GetBuffer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyObject_GetBuffer()</span></code></a>.</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 <a class="reference internal" href="#c.Py_buffer.format" title="Py_buffer.format"><code class="xref c c-data docutils literal notranslate"><span class="pre">format</span></code></a>. This function is not yet implemented.</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> order</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>order</em> is <code class="docutils literal notranslate"><span class="pre">'C'</span></code>) or Fortran-style (<em>order</em> is <code class="docutils literal notranslate"><span class="pre">'F'</span></code>) <a class="reference internal" href="../glossary.html#term-contiguous"><span class="xref std std-term">contiguous</span></a> or either one (<em>order</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. This function always succeeds.</p> </dd></dl> <dl class="function"> <dt id="c.PyBuffer_ToContiguous"> int <code class="descname">PyBuffer_ToContiguous</code><span class="sig-paren">(</span>void<em> *buf</em>, <a class="reference internal" href="#c.Py_buffer" title="Py_buffer">Py_buffer</a><em> *src</em>, Py_ssize_t<em> len</em>, char<em> order</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_ToContiguous" title="Permalink to this definition">¶</a></dt> <dd><p>Copy <em>len</em> bytes from <em>src</em> to its contiguous representation in <em>buf</em>. <em>order</em> can be <code class="docutils literal notranslate"><span class="pre">'C'</span></code> or <code class="docutils literal notranslate"><span class="pre">'F'</span></code> (for C-style or Fortran-style ordering). <code class="docutils literal notranslate"><span class="pre">0</span></code> is returned on success, <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p> <p>This function fails if <em>len</em> != <em>src->len</em>.</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> order</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 <a class="reference internal" href="../glossary.html#term-contiguous"><span class="xref std std-term">contiguous</span></a> (C-style if <em>order</em> is <code class="docutils literal notranslate"><span class="pre">'C'</span></code> or Fortran-style if <em>order</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> *exporter</em>, void<em> *buf</em>, Py_ssize_t<em> len</em>, int<em> readonly</em>, int<em> flags</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyBuffer_FillInfo" title="Permalink to this definition">¶</a></dt> <dd><p>Handle buffer requests for an exporter that wants to expose <em>buf</em> of size <em>len</em> with writability set according to <em>readonly</em>. <em>buf</em> is interpreted as a sequence of unsigned bytes.</p> <p>The <em>flags</em> argument indicates the request type. This function always fills in <em>view</em> as specified by flags, unless <em>buf</em> has been designated as read-only and <a class="reference internal" href="#c.PyBUF_WRITABLE" title="PyBUF_WRITABLE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PyBUF_WRITABLE</span></code></a> is set in <em>flags</em>.</p> <p>On success, set <code class="xref c c-member docutils literal notranslate"><span class="pre">view->obj</span></code> to a new reference to <em>exporter</em> and return 0. Otherwise, raise <code class="xref c c-data docutils literal notranslate"><span class="pre">PyExc_BufferError</span></code>, set <code class="xref c c-member docutils literal notranslate"><span class="pre">view->obj</span></code> to <em>NULL</em> and return <code class="docutils literal notranslate"><span class="pre">-1</span></code>;</p> <p>If this function is used as part of a <a class="reference internal" href="typeobj.html#buffer-structs"><span class="std std-ref">getbufferproc</span></a>, <em>exporter</em> MUST be set to the exporting object and <em>flags</em> must be passed unmodified. Otherwise, <em>exporter</em> MUST be NULL.</p> </dd></dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">Buffer Protocol</a><ul> <li><a class="reference internal" href="#buffer-structure">Buffer structure</a></li> <li><a class="reference internal" href="#buffer-request-types">Buffer request types</a><ul> <li><a class="reference internal" href="#request-independent-fields">request-independent fields</a></li> <li><a class="reference internal" href="#readonly-format">readonly, format</a></li> <li><a class="reference internal" href="#shape-strides-suboffsets">shape, strides, suboffsets</a></li> <li><a class="reference internal" href="#contiguity-requests">contiguity requests</a></li> <li><a class="reference internal" href="#compound-requests">compound requests</a></li> </ul> </li> <li><a class="reference internal" href="#complex-arrays">Complex arrays</a><ul> <li><a class="reference internal" href="#numpy-style-shape-and-strides">NumPy-style: shape and strides</a></li> <li><a class="reference internal" href="#pil-style-shape-strides-and-suboffsets">PIL-style: shape, strides and suboffsets</a></li> </ul> </li> <li><a class="reference internal" href="#buffer-related-functions">Buffer-related functions</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="iter.html" title="previous chapter">Iterator Protocol</a></p> <h4>Next topic</h4> <p class="topless"><a href="objbuffer.html" title="next chapter">Old Buffer Protocol</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.7/Doc/c-api/buffer.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="objbuffer.html" title="Old Buffer Protocol" >next</a> |</li> <li class="right" > <a href="iter.html" title="Iterator Protocol" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <span class="language_switcher_placeholder">en</span> <span class="version_switcher_placeholder">3.7.4</span> <a href="../index.html">Documentation </a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li> <li class="nav-item nav-item-2"><a href="abstract.html" >Abstract Objects Layer</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 2001-2019, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on Jul 13, 2019. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.0.1. </div> </body> </html>