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<div class="section" id="common-object-structures">
<span id="common-structs"></span><h1>Common Object Structures<a class="headerlink" href="#common-object-structures" title="Permalink to this headline">¶</a></h1>
<p>There are a large number of structures which are used in the definition of
object types for Python. This section describes these structures and how they
are used.</p>
<p>All Python objects ultimately share a small number of fields at the beginning
of the object’s representation in memory. These are represented by the
<a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> and <a class="reference internal" href="#c.PyVarObject" title="PyVarObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyVarObject</span></code></a> types, which are defined, in turn,
by the expansions of some macros also used, whether directly or indirectly, in
the definition of all other Python objects.</p>
<dl class="type">
<dt id="c.PyObject">
<code class="sig-name descname">PyObject</code><a class="headerlink" href="#c.PyObject" title="Permalink to this definition">¶</a></dt>
<dd><p>All object types are extensions of this type. This is a type which
contains the information Python needs to treat a pointer to an object as an
object. In a normal “release” build, it contains only the object’s
reference count and a pointer to the corresponding type object.
Nothing is actually declared to be a <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a>, but every pointer
to a Python object can be cast to a <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a>. Access to the
members must be done by using the macros <a class="reference internal" href="#c.Py_REFCNT" title="Py_REFCNT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_REFCNT</span></code></a> and
<a class="reference internal" href="#c.Py_TYPE" title="Py_TYPE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_TYPE</span></code></a>.</p>
</dd></dl>
<dl class="type">
<dt id="c.PyVarObject">
<code class="sig-name descname">PyVarObject</code><a class="headerlink" href="#c.PyVarObject" title="Permalink to this definition">¶</a></dt>
<dd><p>This is an extension of <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> that adds the <code class="xref py py-attr docutils literal notranslate"><span class="pre">ob_size</span></code>
field. This is only used for objects that have some notion of <em>length</em>.
This type does not often appear in the Python/C API.
Access to the members must be done by using the macros
<a class="reference internal" href="#c.Py_REFCNT" title="Py_REFCNT"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_REFCNT</span></code></a>, <a class="reference internal" href="#c.Py_TYPE" title="Py_TYPE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_TYPE</span></code></a>, and <a class="reference internal" href="#c.Py_SIZE" title="Py_SIZE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">Py_SIZE</span></code></a>.</p>
</dd></dl>
<dl class="macro">
<dt id="c.PyObject_HEAD">
<code class="sig-name descname">PyObject_HEAD</code><a class="headerlink" href="#c.PyObject_HEAD" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a macro used when declaring new types which represent objects
without a varying length. The PyObject_HEAD macro expands to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyObject</span> <span class="n">ob_base</span><span class="p">;</span>
</pre></div>
</div>
<p>See documentation of <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> above.</p>
</dd></dl>
<dl class="macro">
<dt id="c.PyObject_VAR_HEAD">
<code class="sig-name descname">PyObject_VAR_HEAD</code><a class="headerlink" href="#c.PyObject_VAR_HEAD" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a macro used when declaring new types which represent objects
with a length that varies from instance to instance.
The PyObject_VAR_HEAD macro expands to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PyVarObject</span> <span class="n">ob_base</span><span class="p">;</span>
</pre></div>
</div>
<p>See documentation of <a class="reference internal" href="#c.PyVarObject" title="PyVarObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyVarObject</span></code></a> above.</p>
</dd></dl>
<dl class="macro">
<dt id="c.Py_TYPE">
<code class="sig-name descname">Py_TYPE</code><span class="sig-paren">(</span>o<span class="sig-paren">)</span><a class="headerlink" href="#c.Py_TYPE" title="Permalink to this definition">¶</a></dt>
<dd><p>This macro is used to access the <code class="xref py py-attr docutils literal notranslate"><span class="pre">ob_type</span></code> member of a Python object.
It expands to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="p">(((</span><span class="n">PyObject</span><span class="o">*</span><span class="p">)(</span><span class="n">o</span><span class="p">))</span><span class="o">-></span><span class="n">ob_type</span><span class="p">)</span>
</pre></div>
</div>
</dd></dl>
<dl class="macro">
<dt id="c.Py_REFCNT">
<code class="sig-name descname">Py_REFCNT</code><span class="sig-paren">(</span>o<span class="sig-paren">)</span><a class="headerlink" href="#c.Py_REFCNT" title="Permalink to this definition">¶</a></dt>
<dd><p>This macro is used to access the <code class="xref py py-attr docutils literal notranslate"><span class="pre">ob_refcnt</span></code> member of a Python
object.
It expands to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="p">(((</span><span class="n">PyObject</span><span class="o">*</span><span class="p">)(</span><span class="n">o</span><span class="p">))</span><span class="o">-></span><span class="n">ob_refcnt</span><span class="p">)</span>
</pre></div>
</div>
</dd></dl>
<dl class="macro">
<dt id="c.Py_SIZE">
<code class="sig-name descname">Py_SIZE</code><span class="sig-paren">(</span>o<span class="sig-paren">)</span><a class="headerlink" href="#c.Py_SIZE" title="Permalink to this definition">¶</a></dt>
<dd><p>This macro is used to access the <code class="xref py py-attr docutils literal notranslate"><span class="pre">ob_size</span></code> member of a Python object.
It expands to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="p">(((</span><span class="n">PyVarObject</span><span class="o">*</span><span class="p">)(</span><span class="n">o</span><span class="p">))</span><span class="o">-></span><span class="n">ob_size</span><span class="p">)</span>
</pre></div>
</div>
</dd></dl>
<dl class="macro">
<dt id="c.PyObject_HEAD_INIT">
<code class="sig-name descname">PyObject_HEAD_INIT</code><span class="sig-paren">(</span>type<span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_HEAD_INIT" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a macro which expands to initialization values for a new
<a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> type. This macro expands to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">_PyObject_EXTRA_INIT</span>
<span class="mi">1</span><span class="p">,</span> <span class="n">type</span><span class="p">,</span>
</pre></div>
</div>
</dd></dl>
<dl class="macro">
<dt id="c.PyVarObject_HEAD_INIT">
<code class="sig-name descname">PyVarObject_HEAD_INIT</code><span class="sig-paren">(</span>type, size<span class="sig-paren">)</span><a class="headerlink" href="#c.PyVarObject_HEAD_INIT" title="Permalink to this definition">¶</a></dt>
<dd><p>This is a macro which expands to initialization values for a new
<a class="reference internal" href="#c.PyVarObject" title="PyVarObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyVarObject</span></code></a> type, including the <code class="xref py py-attr docutils literal notranslate"><span class="pre">ob_size</span></code> field.
This macro expands to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">_PyObject_EXTRA_INIT</span>
<span class="mi">1</span><span class="p">,</span> <span class="n">type</span><span class="p">,</span> <span class="n">size</span><span class="p">,</span>
</pre></div>
</div>
</dd></dl>
<dl class="type">
<dt id="c.PyCFunction">
<code class="sig-name descname">PyCFunction</code><a class="headerlink" href="#c.PyCFunction" title="Permalink to this definition">¶</a></dt>
<dd><p>Type of the functions used to implement most Python callables in C.
Functions of this type take two <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a> parameters and return
one such value. If the return value is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, an exception shall have
been set. If not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the return value is interpreted as the return
value of the function as exposed in Python. The function must return a new
reference.</p>
</dd></dl>
<dl class="type">
<dt id="c.PyCFunctionWithKeywords">
<code class="sig-name descname">PyCFunctionWithKeywords</code><a class="headerlink" href="#c.PyCFunctionWithKeywords" title="Permalink to this definition">¶</a></dt>
<dd><p>Type of the functions used to implement Python callables in C
with signature <code class="xref py py-const docutils literal notranslate"><span class="pre">METH_VARARGS</span> <span class="pre">|</span> <span class="pre">METH_KEYWORDS</span></code>.</p>
</dd></dl>
<dl class="type">
<dt id="c._PyCFunctionFast">
<code class="sig-name descname">_PyCFunctionFast</code><a class="headerlink" href="#c._PyCFunctionFast" title="Permalink to this definition">¶</a></dt>
<dd><p>Type of the functions used to implement Python callables in C
with signature <a class="reference internal" href="#METH_FASTCALL" title="METH_FASTCALL"><code class="xref py py-const docutils literal notranslate"><span class="pre">METH_FASTCALL</span></code></a>.</p>
</dd></dl>
<dl class="type">
<dt id="c._PyCFunctionFastWithKeywords">
<code class="sig-name descname">_PyCFunctionFastWithKeywords</code><a class="headerlink" href="#c._PyCFunctionFastWithKeywords" title="Permalink to this definition">¶</a></dt>
<dd><p>Type of the functions used to implement Python callables in C
with signature <code class="xref py py-const docutils literal notranslate"><span class="pre">METH_FASTCALL</span> <span class="pre">|</span> <span class="pre">METH_KEYWORDS</span></code>.</p>
</dd></dl>
<dl class="type">
<dt id="c.PyMethodDef">
<code class="sig-name descname">PyMethodDef</code><a class="headerlink" href="#c.PyMethodDef" title="Permalink to this definition">¶</a></dt>
<dd><p>Structure used to describe a method of an extension type. This structure has
four fields:</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 28%" />
<col style="width: 23%" />
<col style="width: 48%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Field</p></th>
<th class="head"><p>C Type</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">ml_name</span></code></p></td>
<td><p>const char *</p></td>
<td><p>name of the method</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">ml_meth</span></code></p></td>
<td><p>PyCFunction</p></td>
<td><p>pointer to the C
implementation</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">ml_flags</span></code></p></td>
<td><p>int</p></td>
<td><p>flag bits indicating how the
call should be constructed</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">ml_doc</span></code></p></td>
<td><p>const char *</p></td>
<td><p>points to the contents of the
docstring</p></td>
</tr>
</tbody>
</table>
</dd></dl>
<p>The <code class="xref py py-attr docutils literal notranslate"><span class="pre">ml_meth</span></code> is a C function pointer. The functions may be of different
types, but they always return <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a>. If the function is not of
the <a class="reference internal" href="#c.PyCFunction" title="PyCFunction"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCFunction</span></code></a>, the compiler will require a cast in the method table.
Even though <a class="reference internal" href="#c.PyCFunction" title="PyCFunction"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCFunction</span></code></a> defines the first parameter as
<a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a>, it is common that the method implementation uses the
specific C type of the <em>self</em> object.</p>
<p>The <code class="xref py py-attr docutils literal notranslate"><span class="pre">ml_flags</span></code> field is a bitfield which can include the following flags.
The individual flags indicate either a calling convention or a binding
convention.</p>
<p>There are four basic calling conventions for positional arguments
and two of them can be combined with <code class="xref py py-const docutils literal notranslate"><span class="pre">METH_KEYWORDS</span></code> to support
also keyword arguments. So there are a total of 6 calling conventions:</p>
<dl class="data">
<dt id="METH_VARARGS">
<code class="sig-name descname">METH_VARARGS</code><a class="headerlink" href="#METH_VARARGS" title="Permalink to this definition">¶</a></dt>
<dd><p>This is the typical calling convention, where the methods have the type
<a class="reference internal" href="#c.PyCFunction" title="PyCFunction"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCFunction</span></code></a>. The function expects two <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a> values.
The first one is the <em>self</em> object for methods; for module functions, it is
the module object. The second parameter (often called <em>args</em>) is a tuple
object representing all arguments. This parameter is typically processed
using <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 <a class="reference internal" href="arg.html#c.PyArg_UnpackTuple" title="PyArg_UnpackTuple"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyArg_UnpackTuple()</span></code></a>.</p>
</dd></dl>
<dl class="data">
<dt>
<code class="sig-name descname">METH_VARARGS | METH_KEYWORDS</code></dt>
<dd><p>Methods with these flags must be of type <a class="reference internal" href="#c.PyCFunctionWithKeywords" title="PyCFunctionWithKeywords"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCFunctionWithKeywords</span></code></a>.
The function expects three parameters: <em>self</em>, <em>args</em>, <em>kwargs</em> where
<em>kwargs</em> is a dictionary of all the keyword arguments or possibly <code class="docutils literal notranslate"><span class="pre">NULL</span></code>
if there are no keyword arguments. The parameters are typically processed
using <a class="reference internal" href="arg.html#c.PyArg_ParseTupleAndKeywords" title="PyArg_ParseTupleAndKeywords"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyArg_ParseTupleAndKeywords()</span></code></a>.</p>
</dd></dl>
<dl class="data">
<dt id="METH_FASTCALL">
<code class="sig-name descname">METH_FASTCALL</code><a class="headerlink" href="#METH_FASTCALL" title="Permalink to this definition">¶</a></dt>
<dd><p>Fast calling convention supporting only positional arguments.
The methods have the type <a class="reference internal" href="#c._PyCFunctionFast" title="_PyCFunctionFast"><code class="xref c c-type docutils literal notranslate"><span class="pre">_PyCFunctionFast</span></code></a>.
The first parameter is <em>self</em>, the second parameter is a C array
of <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a> values indicating the arguments and the third
parameter is the number of arguments (the length of the array).</p>
<p>This is not part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">limited API</span></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt>
<code class="sig-name descname">METH_FASTCALL | METH_KEYWORDS</code></dt>
<dd><p>Extension of <a class="reference internal" href="#METH_FASTCALL" title="METH_FASTCALL"><code class="xref py py-const docutils literal notranslate"><span class="pre">METH_FASTCALL</span></code></a> supporting also keyword arguments,
with methods of type <a class="reference internal" href="#c._PyCFunctionFastWithKeywords" title="_PyCFunctionFastWithKeywords"><code class="xref c c-type docutils literal notranslate"><span class="pre">_PyCFunctionFastWithKeywords</span></code></a>.
Keyword arguments are passed the same way as in the vectorcall protocol:
there is an additional fourth <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a> parameter
which is a tuple representing the names of the keyword arguments
or possibly <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if there are no keywords. The values of the keyword
arguments are stored in the <em>args</em> array, after the positional arguments.</p>
<p>This is not part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">limited API</span></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="METH_NOARGS">
<code class="sig-name descname">METH_NOARGS</code><a class="headerlink" href="#METH_NOARGS" title="Permalink to this definition">¶</a></dt>
<dd><p>Methods without parameters don’t need to check whether arguments are given if
they are listed with the <a class="reference internal" href="#METH_NOARGS" title="METH_NOARGS"><code class="xref py py-const docutils literal notranslate"><span class="pre">METH_NOARGS</span></code></a> flag. They need to be of type
<a class="reference internal" href="#c.PyCFunction" title="PyCFunction"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCFunction</span></code></a>. The first parameter is typically named <em>self</em> and will
hold a reference to the module or object instance. In all cases the second
parameter will be <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
</dd></dl>
<dl class="data">
<dt id="METH_O">
<code class="sig-name descname">METH_O</code><a class="headerlink" href="#METH_O" title="Permalink to this definition">¶</a></dt>
<dd><p>Methods with a single object argument can be listed with the <a class="reference internal" href="#METH_O" title="METH_O"><code class="xref py py-const docutils literal notranslate"><span class="pre">METH_O</span></code></a>
flag, instead of invoking <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> with a <code class="docutils literal notranslate"><span class="pre">"O"</span></code> argument.
They have the type <a class="reference internal" href="#c.PyCFunction" title="PyCFunction"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCFunction</span></code></a>, with the <em>self</em> parameter, and a
<a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a> parameter representing the single argument.</p>
</dd></dl>
<p>These two constants are not used to indicate the calling convention but the
binding when use with methods of classes. These may not be used for functions
defined for modules. At most one of these flags may be set for any given
method.</p>
<dl class="data">
<dt id="METH_CLASS">
<code class="sig-name descname">METH_CLASS</code><a class="headerlink" href="#METH_CLASS" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-0">The method will be passed the type object as the first parameter rather
than an instance of the type. This is used to create <em>class methods</em>,
similar to what is created when using the <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">classmethod()</span></code></a> built-in
function.</p>
</dd></dl>
<dl class="data">
<dt id="METH_STATIC">
<code class="sig-name descname">METH_STATIC</code><a class="headerlink" href="#METH_STATIC" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-1">The method will be passed <code class="docutils literal notranslate"><span class="pre">NULL</span></code> as the first parameter rather than an
instance of the type. This is used to create <em>static methods</em>, similar to
what is created when using the <a class="reference internal" href="../library/functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">staticmethod()</span></code></a> built-in function.</p>
</dd></dl>
<p>One other constant controls whether a method is loaded in place of another
definition with the same method name.</p>
<dl class="data">
<dt id="METH_COEXIST">
<code class="sig-name descname">METH_COEXIST</code><a class="headerlink" href="#METH_COEXIST" title="Permalink to this definition">¶</a></dt>
<dd><p>The method will be loaded in place of existing definitions. Without
<em>METH_COEXIST</em>, the default is to skip repeated definitions. Since slot
wrappers are loaded before the method table, the existence of a
<em>sq_contains</em> slot, for example, would generate a wrapped method named
<a class="reference internal" href="../reference/datamodel.html#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__contains__()</span></code></a> and preclude the loading of a corresponding
PyCFunction with the same name. With the flag defined, the PyCFunction
will be loaded in place of the wrapper object and will co-exist with the
slot. This is helpful because calls to PyCFunctions are optimized more
than wrapper object calls.</p>
</dd></dl>
<dl class="type">
<dt id="c.PyMemberDef">
<code class="sig-name descname">PyMemberDef</code><a class="headerlink" href="#c.PyMemberDef" title="Permalink to this definition">¶</a></dt>
<dd><p>Structure which describes an attribute of a type which corresponds to a C
struct member. Its fields are:</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 28%" />
<col style="width: 23%" />
<col style="width: 48%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Field</p></th>
<th class="head"><p>C Type</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">name</span></code></p></td>
<td><p>const char *</p></td>
<td><p>name of the member</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">type</span></code></p></td>
<td><p>int</p></td>
<td><p>the type of the member in the
C struct</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">offset</span></code></p></td>
<td><p>Py_ssize_t</p></td>
<td><p>the offset in bytes that the
member is located on the
type’s object struct</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">flags</span></code></p></td>
<td><p>int</p></td>
<td><p>flag bits indicating if the
field should be read-only or
writable</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">doc</span></code></p></td>
<td><p>const char *</p></td>
<td><p>points to the contents of the
docstring</p></td>
</tr>
</tbody>
</table>
<p><code class="xref py py-attr docutils literal notranslate"><span class="pre">type</span></code> can be one of many <code class="docutils literal notranslate"><span class="pre">T_</span></code> macros corresponding to various C
types. When the member is accessed in Python, it will be converted to the
equivalent Python type.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 45%" />
<col style="width: 55%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Macro name</p></th>
<th class="head"><p>C type</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>T_SHORT</p></td>
<td><p>short</p></td>
</tr>
<tr class="row-odd"><td><p>T_INT</p></td>
<td><p>int</p></td>
</tr>
<tr class="row-even"><td><p>T_LONG</p></td>
<td><p>long</p></td>
</tr>
<tr class="row-odd"><td><p>T_FLOAT</p></td>
<td><p>float</p></td>
</tr>
<tr class="row-even"><td><p>T_DOUBLE</p></td>
<td><p>double</p></td>
</tr>
<tr class="row-odd"><td><p>T_STRING</p></td>
<td><p>const char *</p></td>
</tr>
<tr class="row-even"><td><p>T_OBJECT</p></td>
<td><p>PyObject *</p></td>
</tr>
<tr class="row-odd"><td><p>T_OBJECT_EX</p></td>
<td><p>PyObject *</p></td>
</tr>
<tr class="row-even"><td><p>T_CHAR</p></td>
<td><p>char</p></td>
</tr>
<tr class="row-odd"><td><p>T_BYTE</p></td>
<td><p>char</p></td>
</tr>
<tr class="row-even"><td><p>T_UBYTE</p></td>
<td><p>unsigned char</p></td>
</tr>
<tr class="row-odd"><td><p>T_UINT</p></td>
<td><p>unsigned int</p></td>
</tr>
<tr class="row-even"><td><p>T_USHORT</p></td>
<td><p>unsigned short</p></td>
</tr>
<tr class="row-odd"><td><p>T_ULONG</p></td>
<td><p>unsigned long</p></td>
</tr>
<tr class="row-even"><td><p>T_BOOL</p></td>
<td><p>char</p></td>
</tr>
<tr class="row-odd"><td><p>T_LONGLONG</p></td>
<td><p>long long</p></td>
</tr>
<tr class="row-even"><td><p>T_ULONGLONG</p></td>
<td><p>unsigned long long</p></td>
</tr>
<tr class="row-odd"><td><p>T_PYSSIZET</p></td>
<td><p>Py_ssize_t</p></td>
</tr>
</tbody>
</table>
<p><code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT</span></code> and <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT_EX</span></code> differ in that
<code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT</span></code> returns <code class="docutils literal notranslate"><span class="pre">None</span></code> if the member is <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and
<code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT_EX</span></code> raises an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AttributeError</span></code></a>. Try to use
<code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT_EX</span></code> over <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT</span></code> because <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT_EX</span></code>
handles use of the <a class="reference internal" href="../reference/simple_stmts.html#del"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">del</span></code></a> statement on that attribute more correctly
than <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT</span></code>.</p>
<p><code class="xref py py-attr docutils literal notranslate"><span class="pre">flags</span></code> can be <code class="docutils literal notranslate"><span class="pre">0</span></code> for write and read access or <code class="xref c c-macro docutils literal notranslate"><span class="pre">READONLY</span></code> for
read-only access. Using <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_STRING</span></code> for <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-attr docutils literal notranslate"><span class="pre">type</span></code></a> implies
<code class="xref c c-macro docutils literal notranslate"><span class="pre">READONLY</span></code>. <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_STRING</span></code> data is interpreted as UTF-8.
Only <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT</span></code> and <code class="xref c c-macro docutils literal notranslate"><span class="pre">T_OBJECT_EX</span></code>
members can be deleted. (They are set to <code class="docutils literal notranslate"><span class="pre">NULL</span></code>).</p>
</dd></dl>
<dl class="type">
<dt id="c.PyGetSetDef">
<code class="sig-name descname">PyGetSetDef</code><a class="headerlink" href="#c.PyGetSetDef" title="Permalink to this definition">¶</a></dt>
<dd><p>Structure to define property-like access for a type. See also description of
the <a class="reference internal" href="typeobj.html#c.PyTypeObject.tp_getset" title="PyTypeObject.tp_getset"><code class="xref c c-member docutils literal notranslate"><span class="pre">PyTypeObject.tp_getset</span></code></a> slot.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 20%" />
<col style="width: 27%" />
<col style="width: 53%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Field</p></th>
<th class="head"><p>C Type</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>name</p></td>
<td><p>const char *</p></td>
<td><p>attribute name</p></td>
</tr>
<tr class="row-odd"><td><p>get</p></td>
<td><p>getter</p></td>
<td><p>C Function to get the attribute</p></td>
</tr>
<tr class="row-even"><td><p>set</p></td>
<td><p>setter</p></td>
<td><p>optional C function to set or
delete the attribute, if omitted
the attribute is readonly</p></td>
</tr>
<tr class="row-odd"><td><p>doc</p></td>
<td><p>const char *</p></td>
<td><p>optional docstring</p></td>
</tr>
<tr class="row-even"><td><p>closure</p></td>
<td><p>void *</p></td>
<td><p>optional function pointer,
providing additional data for
getter and setter</p></td>
</tr>
</tbody>
</table>
<p>The <code class="docutils literal notranslate"><span class="pre">get</span></code> function takes one <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a> parameter (the
instance) and a function pointer (the associated <code class="docutils literal notranslate"><span class="pre">closure</span></code>):</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span> <span class="n">PyObject</span> <span class="o">*</span><span class="p">(</span><span class="o">*</span><span class="n">getter</span><span class="p">)(</span><span class="n">PyObject</span> <span class="o">*</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="p">);</span>
</pre></div>
</div>
<p>It should return a new reference on success or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> with a set exception
on failure.</p>
<p><code class="docutils literal notranslate"><span class="pre">set</span></code> functions take two <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject*</span></code></a> parameters (the instance and
the value to be set) and a function pointer (the associated <code class="docutils literal notranslate"><span class="pre">closure</span></code>):</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span> <span class="nf">int</span> <span class="p">(</span><span class="o">*</span><span class="n">setter</span><span class="p">)(</span><span class="n">PyObject</span> <span class="o">*</span><span class="p">,</span> <span class="n">PyObject</span> <span class="o">*</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="p">);</span>
</pre></div>
</div>
<p>In case the attribute should be deleted the second parameter is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.
Should return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success or <code class="docutils literal notranslate"><span class="pre">-1</span></code> with a set exception on failure.</p>
</dd></dl>
</div>
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