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<li><a class="reference internal" href="#">Common Object Structures</a><ul>
<li><a class="reference internal" href="#base-object-types-and-macros">Base object types and macros</a></li>
<li><a class="reference internal" href="#implementing-functions-and-methods">Implementing functions and methods</a></li>
<li><a class="reference internal" href="#accessing-attributes-of-extension-types">Accessing attributes of extension types</a></li>
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 <section id="common-object-structures">
<h1>Common Object Structures<a class="headerlink" href="#common-object-structures" title="Permalink to this headline">¶</a></h1>
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.
<section id="base-object-types-and-macros">
<h2>Base object types and macros<a class="headerlink" href="#base-object-types-and-macros" title="Permalink to this headline">¶</a></h2>
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">PyObject</code></a> and <a class="reference internal" href="#c.PyVarObject" title="PyVarObject"><code class="xref c c-type docutils literal notranslate">PyVarObject</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.
<dl class="c type">
<dt class="sig sig-object c" id="c.PyObject">
type PyObject<a class="headerlink" href="#c.PyObject" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Limited API</a>. (Only some members are part of the stable ABI.)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">PyObject</code></a>, but every pointer
to a Python object can be cast to a <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</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">Py_REFCNT</code></a> and
<a class="reference internal" href="#c.Py_TYPE" title="Py_TYPE"><code class="xref c c-macro docutils literal notranslate">Py_TYPE</code></a>.
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.PyVarObject">
type PyVarObject<a class="headerlink" href="#c.PyVarObject" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Limited API</a>. (Only some members are part of the stable ABI.)This is an extension of <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate">PyObject</code></a> that adds the <code class="xref py py-attr docutils literal notranslate">ob_size</code>
field. This is only used for objects that have some notion of length.
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">Py_REFCNT</code></a>, <a class="reference internal" href="#c.Py_TYPE" title="Py_TYPE"><code class="xref c c-macro docutils literal notranslate">Py_TYPE</code></a>, and <a class="reference internal" href="#c.Py_SIZE" title="Py_SIZE"><code class="xref c c-macro docutils literal notranslate">Py_SIZE</code></a>.
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyObject_HEAD">
PyObject_HEAD<a class="headerlink" href="#c.PyObject_HEAD" title="Permalink to this definition">¶</a> </dt>
<dd>This is a macro used when declaring new types which represent objects
without a varying length. The PyObject_HEAD macro expands to:
<div class="highlight-c notranslate"><div class="highlight"><pre>PyObject ob_base;
</pre></div>
</div>
See documentation of <a class="reference internal" href="#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate">PyObject</code></a> above.
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyObject_VAR_HEAD">
PyObject_VAR_HEAD<a class="headerlink" href="#c.PyObject_VAR_HEAD" title="Permalink to this definition">¶</a> </dt>
<dd>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:
<div class="highlight-c notranslate"><div class="highlight"><pre>PyVarObject ob_base;
</pre></div>
</div>
See documentation of <a class="reference internal" href="#c.PyVarObject" title="PyVarObject"><code class="xref c c-type docutils literal notranslate">PyVarObject</code></a> above.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_Is">
int Py_Is(const <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *x, const <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *y)<a class="headerlink" href="#c.Py_Is" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> since version 3.10.Test if the x object is the y object, the same as <code class="docutils literal notranslate">x is y</code> in Python.
<div class="versionadded">
New in version 3.10.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_IsNone">
int Py_IsNone(const <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *x)<a class="headerlink" href="#c.Py_IsNone" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> since version 3.10.Test if an object is the <code class="docutils literal notranslate">None</code> singleton,
the same as <code class="docutils literal notranslate">x is None</code> in Python.
<div class="versionadded">
New in version 3.10.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_IsTrue">
int Py_IsTrue(const <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *x)<a class="headerlink" href="#c.Py_IsTrue" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> since version 3.10.Test if an object is the <code class="docutils literal notranslate">True</code> singleton,
the same as <code class="docutils literal notranslate">x is True</code> in Python.
<div class="versionadded">
New in version 3.10.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_IsFalse">
int Py_IsFalse(const <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *x)<a class="headerlink" href="#c.Py_IsFalse" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> since version 3.10.Test if an object is the <code class="docutils literal notranslate">False</code> singleton,
the same as <code class="docutils literal notranslate">x is False</code> in Python.
<div class="versionadded">
New in version 3.10.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_TYPE">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> *Py_TYPE(const <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_TYPE" title="Permalink to this definition">¶</a> </dt>
<dd>Get the type of the Python object o.
Return a <a class="reference internal" href="../glossary.html#term-borrowed-reference">borrowed reference</a>.
Use the <a class="reference internal" href="#c.Py_SET_TYPE" title="Py_SET_TYPE"><code class="xref c c-func docutils literal notranslate">Py_SET_TYPE()</code></a> function to set an object type.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_IS_TYPE">
int Py_IS_TYPE(<a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *o, <a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> *type)<a class="headerlink" href="#c.Py_IS_TYPE" title="Permalink to this definition">¶</a> </dt>
<dd>Return non-zero if the object o type is type. Return zero otherwise.
Equivalent to: <code class="docutils literal notranslate">Py_TYPE(o) == type</code>.
<div class="versionadded">
New in version 3.9.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_SET_TYPE">
void Py_SET_TYPE(<a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *o, <a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> *type)<a class="headerlink" href="#c.Py_SET_TYPE" title="Permalink to this definition">¶</a> </dt>
<dd>Set the object o type to type.
<div class="versionadded">
New in version 3.9.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_REFCNT">
<a class="reference internal" href="intro.html#c.Py_ssize_t" title="Py_ssize_t">Py_ssize_t</a> Py_REFCNT(const <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_REFCNT" title="Permalink to this definition">¶</a> </dt>
<dd>Get the reference count of the Python object o.
<div class="versionchanged">
Changed in version 3.10: <a class="reference internal" href="#c.Py_REFCNT" title="Py_REFCNT"><code class="xref c c-func docutils literal notranslate">Py_REFCNT()</code></a> is changed to the inline static function.
Use <a class="reference internal" href="#c.Py_SET_REFCNT" title="Py_SET_REFCNT"><code class="xref c c-func docutils literal notranslate">Py_SET_REFCNT()</code></a> to set an object reference count.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_SET_REFCNT">
void Py_SET_REFCNT(<a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *o, <a class="reference internal" href="intro.html#c.Py_ssize_t" title="Py_ssize_t">Py_ssize_t</a> refcnt)<a class="headerlink" href="#c.Py_SET_REFCNT" title="Permalink to this definition">¶</a> </dt>
<dd>Set the object o reference counter to refcnt.
<div class="versionadded">
New in version 3.9.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_SIZE">
<a class="reference internal" href="intro.html#c.Py_ssize_t" title="Py_ssize_t">Py_ssize_t</a> Py_SIZE(const <a class="reference internal" href="#c.PyVarObject" title="PyVarObject">PyVarObject</a> *o)<a class="headerlink" href="#c.Py_SIZE" title="Permalink to this definition">¶</a> </dt>
<dd>Get the size of the Python object o.
Use the <a class="reference internal" href="#c.Py_SET_SIZE" title="Py_SET_SIZE"><code class="xref c c-func docutils literal notranslate">Py_SET_SIZE()</code></a> function to set an object size.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_SET_SIZE">
void Py_SET_SIZE(<a class="reference internal" href="#c.PyVarObject" title="PyVarObject">PyVarObject</a> *o, <a class="reference internal" href="intro.html#c.Py_ssize_t" title="Py_ssize_t">Py_ssize_t</a> size)<a class="headerlink" href="#c.Py_SET_SIZE" title="Permalink to this definition">¶</a> </dt>
<dd>Set the object o size to size.
<div class="versionadded">
New in version 3.9.
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyObject_HEAD_INIT">
PyObject_HEAD_INIT(type)<a class="headerlink" href="#c.PyObject_HEAD_INIT" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyObject</code></a> type. This macro expands to:
<div class="highlight-c notranslate"><div class="highlight"><pre>_PyObject_EXTRA_INIT
1, type,
</pre></div>
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.PyVarObject_HEAD_INIT">
PyVarObject_HEAD_INIT(type, size)<a class="headerlink" href="#c.PyVarObject_HEAD_INIT" title="Permalink to this definition">¶</a> </dt>
<dd>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">PyVarObject</code></a> type, including the <code class="xref py py-attr docutils literal notranslate">ob_size</code> field.
This macro expands to:
<div class="highlight-c notranslate"><div class="highlight"><pre>_PyObject_EXTRA_INIT
1, type, size,
</pre></div>
</div>
</dd></dl>

</section>
<section id="implementing-functions-and-methods">
<h2>Implementing functions and methods<a class="headerlink" href="#implementing-functions-and-methods" title="Permalink to this headline">¶</a></h2>
<dl class="c type">
<dt class="sig sig-object c" id="c.PyCFunction">
type PyCFunction<a class="headerlink" href="#c.PyCFunction" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a>.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">PyObject</a>* parameters and return
one such value. If the return value is <code class="docutils literal notranslate">NULL</code>, an exception shall have
been set. If not <code class="docutils literal notranslate">NULL</code>, the return value is interpreted as the return
value of the function as exposed in Python. The function must return a new
reference.
The function signature is:
<div class="highlight-c notranslate"><div class="highlight"><pre>PyObject *PyCFunction(PyObject *self,
 PyObject *args);
</pre></div>
</div>
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.PyCFunctionWithKeywords">
type PyCFunctionWithKeywords<a class="headerlink" href="#c.PyCFunctionWithKeywords" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a>.Type of the functions used to implement Python callables in C
with signature <code class="xref py py-const docutils literal notranslate">METH_VARARGS | METH_KEYWORDS</code>.
The function signature is:
<div class="highlight-c notranslate"><div class="highlight"><pre>PyObject *PyCFunctionWithKeywords(PyObject *self,
 PyObject *args,
 PyObject *kwargs);
</pre></div>
</div>
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c._PyCFunctionFast">
type _PyCFunctionFast<a class="headerlink" href="#c._PyCFunctionFast" title="Permalink to this definition">¶</a> </dt>
<dd>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">METH_FASTCALL</code></a>.
The function signature is:
<div class="highlight-c notranslate"><div class="highlight"><pre>PyObject *_PyCFunctionFast(PyObject *self,
 PyObject *const *args,
 Py_ssize_t nargs);
</pre></div>
</div>
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c._PyCFunctionFastWithKeywords">
type _PyCFunctionFastWithKeywords<a class="headerlink" href="#c._PyCFunctionFastWithKeywords" title="Permalink to this definition">¶</a> </dt>
<dd>Type of the functions used to implement Python callables in C
with signature <code class="xref py py-const docutils literal notranslate">METH_FASTCALL | METH_KEYWORDS</code>.
The function signature is:
<div class="highlight-c notranslate"><div class="highlight"><pre>PyObject *_PyCFunctionFastWithKeywords(PyObject *self,
 PyObject *const *args,
 Py_ssize_t nargs,
 PyObject *kwnames);
</pre></div>
</div>
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.PyCMethod">
type PyCMethod<a class="headerlink" href="#c.PyCMethod" title="Permalink to this definition">¶</a> </dt>
<dd>Type of the functions used to implement Python callables in C
with signature <code class="xref py py-const docutils literal notranslate">METH_METHOD | METH_FASTCALL | METH_KEYWORDS</code>.
The function signature is:
<div class="highlight-c notranslate"><div class="highlight"><pre>PyObject *PyCMethod(PyObject *self,
 PyTypeObject *defining_class,
 PyObject *const *args,
 Py_ssize_t nargs,
 PyObject *kwnames)
</pre></div>
</div>
<div class="versionadded">
New in version 3.9.
</div>
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.PyMethodDef">
type PyMethodDef<a class="headerlink" href="#c.PyMethodDef" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> (including all members).Structure used to describe a method of an extension type. This structure has
four fields:
<dl class="c member">
<dt class="sig sig-object c" id="c.PyMethodDef.ml_name">
const char *ml_name<a class="headerlink" href="#c.PyMethodDef.ml_name" title="Permalink to this definition">¶</a> </dt>
<dd>name of the method
</dd></dl>

<dl class="c member">
<dt class="sig sig-object c" id="c.PyMethodDef.ml_meth">
<a class="reference internal" href="#c.PyCFunction" title="PyCFunction">PyCFunction</a> ml_meth<a class="headerlink" href="#c.PyMethodDef.ml_meth" title="Permalink to this definition">¶</a> </dt>
<dd>pointer to the C implementation
</dd></dl>

<dl class="c member">
<dt class="sig sig-object c" id="c.PyMethodDef.ml_flags">
int ml_flags<a class="headerlink" href="#c.PyMethodDef.ml_flags" title="Permalink to this definition">¶</a> </dt>
<dd>flags bits indicating how the call should be constructed
</dd></dl>

<dl class="c member">
<dt class="sig sig-object c" id="c.PyMethodDef.ml_doc">
const char *ml_doc<a class="headerlink" href="#c.PyMethodDef.ml_doc" title="Permalink to this definition">¶</a> </dt>
<dd>points to the contents of the docstring
</dd></dl>

</dd></dl>

The <code class="xref c c-member docutils literal notranslate">ml_meth</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">PyObject</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">PyCFunction</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">PyCFunction</code></a> defines the first parameter as
<a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a>*, it is common that the method implementation uses the
specific C type of the self object.
The <code class="xref c c-member docutils literal notranslate">ml_flags</code> field is a bitfield which can include the following flags.
The individual flags indicate either a calling convention or a binding
convention.
There are these calling conventions:
<dl class="py data">
<dt class="sig sig-object py" id="METH_VARARGS">
METH_VARARGS<a class="headerlink" href="#METH_VARARGS" title="Permalink to this definition">¶</a></dt>
<dd>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">PyCFunction</code></a>. The function expects two <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a>* values.
The first one is the self object for methods; for module functions, it is
the module object. The second parameter (often called args) 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">PyArg_ParseTuple()</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">PyArg_UnpackTuple()</code></a>.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py">
METH_VARARGS | METH_KEYWORDS</dt>
<dd>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">PyCFunctionWithKeywords</code></a>.
The function expects three parameters: self, args, kwargs where
kwargs is a dictionary of all the keyword arguments or possibly <code class="docutils literal notranslate">NULL</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">PyArg_ParseTupleAndKeywords()</code></a>.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="METH_FASTCALL">
METH_FASTCALL<a class="headerlink" href="#METH_FASTCALL" title="Permalink to this definition">¶</a></dt>
<dd>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">_PyCFunctionFast</code></a>.
The first parameter is self, the second parameter is a C array
of <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a>* values indicating the arguments and the third
parameter is the number of arguments (the length of the array).
<div class="versionadded">
New in version 3.7.
</div>
<div class="versionchanged">
Changed in version 3.10: <code class="docutils literal notranslate">METH_FASTCALL</code> is now part of the stable ABI.
</div>
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py">
METH_FASTCALL | METH_KEYWORDS</dt>
<dd>Extension of <a class="reference internal" href="#METH_FASTCALL" title="METH_FASTCALL"><code class="xref py py-const docutils literal notranslate">METH_FASTCALL</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">_PyCFunctionFastWithKeywords</code></a>.
Keyword arguments are passed the same way as in the
<a class="reference internal" href="call.html#vectorcall">vectorcall protocol</a>:
there is an additional fourth <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a>* parameter
which is a tuple representing the names of the keyword arguments
(which are guaranteed to be strings)
or possibly <code class="docutils literal notranslate">NULL</code> if there are no keywords. The values of the keyword
arguments are stored in the args array, after the positional arguments.
<div class="versionadded">
New in version 3.7.
</div>
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py">
METH_METHOD | METH_FASTCALL | METH_KEYWORDS</dt>
<dd>Extension of <code class="xref py py-const docutils literal notranslate">METH_FASTCALL | METH_KEYWORDS</code> supporting the defining
class, that is, the class that contains the method in question.
The defining class might be a superclass of <code class="docutils literal notranslate">Py_TYPE(self)</code>.
The method needs to be of type <a class="reference internal" href="#c.PyCMethod" title="PyCMethod"><code class="xref c c-type docutils literal notranslate">PyCMethod</code></a>, the same as for
<code class="docutils literal notranslate">METH_FASTCALL | METH_KEYWORDS</code> with <code class="docutils literal notranslate">defining_class</code> argument added after
<code class="docutils literal notranslate">self</code>.
<div class="versionadded">
New in version 3.9.
</div>
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="METH_NOARGS">
METH_NOARGS<a class="headerlink" href="#METH_NOARGS" title="Permalink to this definition">¶</a></dt>
<dd>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">METH_NOARGS</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">PyCFunction</code></a>. The first parameter is typically named self and will
hold a reference to the module or object instance. In all cases the second
parameter will be <code class="docutils literal notranslate">NULL</code>.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="METH_O">
METH_O<a class="headerlink" href="#METH_O" title="Permalink to this definition">¶</a></dt>
<dd>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">METH_O</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">PyArg_ParseTuple()</code></a> with a <code class="docutils literal notranslate">&quot;O&quot;</code> argument.
They have the type <a class="reference internal" href="#c.PyCFunction" title="PyCFunction"><code class="xref c c-type docutils literal notranslate">PyCFunction</code></a>, with the self parameter, and a
<a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a>* parameter representing the single argument.
</dd></dl>

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.
<dl class="py data">
<dt class="sig sig-object py" id="METH_CLASS">
METH_CLASS<a class="headerlink" href="#METH_CLASS" title="Permalink to this definition">¶</a></dt>
<dd>The method will be passed the type object as the first parameter rather
than an instance of the type. This is used to create class methods,
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">classmethod()</code></a> built-in
function.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="METH_STATIC">
METH_STATIC<a class="headerlink" href="#METH_STATIC" title="Permalink to this definition">¶</a></dt>
<dd>The method will be passed <code class="docutils literal notranslate">NULL</code> as the first parameter rather than an
instance of the type. This is used to create static methods, 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">staticmethod()</code></a> built-in function.
</dd></dl>

One other constant controls whether a method is loaded in place of another
definition with the same method name.
<dl class="py data">
<dt class="sig sig-object py" id="METH_COEXIST">
METH_COEXIST<a class="headerlink" href="#METH_COEXIST" title="Permalink to this definition">¶</a></dt>
<dd>The method will be loaded in place of existing definitions. Without
METH_COEXIST, the default is to skip repeated definitions. Since slot
wrappers are loaded before the method table, the existence of a
sq_contains slot, for example, would generate a wrapped method named
<code class="xref py py-meth docutils literal notranslate">__contains__()</code> 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.
</dd></dl>

</section>
<section id="accessing-attributes-of-extension-types">
<h2>Accessing attributes of extension types<a class="headerlink" href="#accessing-attributes-of-extension-types" title="Permalink to this headline">¶</a></h2>
<dl class="c type">
<dt class="sig sig-object c" id="c.PyMemberDef">
type PyMemberDef<a class="headerlink" href="#c.PyMemberDef" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> (including all members).Structure which describes an attribute of a type which corresponds to a C
struct member. Its fields are:
<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">Field</th>
<th class="head">C Type</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><code class="xref py py-attr docutils literal notranslate">name</code></td>
<td>const char *</td>
<td>name of the member</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-attr docutils literal notranslate">type</code></td>
<td>int</td>
<td>the type of the member in the
C struct</td>
</tr>
<tr class="row-even"><td><code class="xref py py-attr docutils literal notranslate">offset</code></td>
<td>Py_ssize_t</td>
<td>the offset in bytes that the
member is located on the
type’s object struct</td>
</tr>
<tr class="row-odd"><td><code class="xref py py-attr docutils literal notranslate">flags</code></td>
<td>int</td>
<td>flag bits indicating if the
field should be read-only or
writable</td>
</tr>
<tr class="row-even"><td><code class="xref py py-attr docutils literal notranslate">doc</code></td>
<td>const char *</td>
<td>points to the contents of the
docstring</td>
</tr>
</tbody>
</table>
<code class="xref py py-attr docutils literal notranslate">type</code> can be one of many <code class="docutils literal notranslate">T_</code> macros corresponding to various C
types. When the member is accessed in Python, it will be converted to the
equivalent Python type.
<table class="docutils align-default">
<colgroup>
<col style="width: 45%" />
<col style="width: 55%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head">Macro name</th>
<th class="head">C type</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td>T_SHORT</td>
<td>short</td>
</tr>
<tr class="row-odd"><td>T_INT</td>
<td>int</td>
</tr>
<tr class="row-even"><td>T_LONG</td>
<td>long</td>
</tr>
<tr class="row-odd"><td>T_FLOAT</td>
<td>float</td>
</tr>
<tr class="row-even"><td>T_DOUBLE</td>
<td>double</td>
</tr>
<tr class="row-odd"><td>T_STRING</td>
<td>const char *</td>
</tr>
<tr class="row-even"><td>T_OBJECT</td>
<td>PyObject *</td>
</tr>
<tr class="row-odd"><td>T_OBJECT_EX</td>
<td>PyObject *</td>
</tr>
<tr class="row-even"><td>T_CHAR</td>
<td>char</td>
</tr>
<tr class="row-odd"><td>T_BYTE</td>
<td>char</td>
</tr>
<tr class="row-even"><td>T_UBYTE</td>
<td>unsigned char</td>
</tr>
<tr class="row-odd"><td>T_UINT</td>
<td>unsigned int</td>
</tr>
<tr class="row-even"><td>T_USHORT</td>
<td>unsigned short</td>
</tr>
<tr class="row-odd"><td>T_ULONG</td>
<td>unsigned long</td>
</tr>
<tr class="row-even"><td>T_BOOL</td>
<td>char</td>
</tr>
<tr class="row-odd"><td>T_LONGLONG</td>
<td>long long</td>
</tr>
<tr class="row-even"><td>T_ULONGLONG</td>
<td>unsigned long long</td>
</tr>
<tr class="row-odd"><td>T_PYSSIZET</td>
<td>Py_ssize_t</td>
</tr>
</tbody>
</table>
<code class="xref c c-macro docutils literal notranslate">T_OBJECT</code> and <code class="xref c c-macro docutils literal notranslate">T_OBJECT_EX</code> differ in that
<code class="xref c c-macro docutils literal notranslate">T_OBJECT</code> returns <code class="docutils literal notranslate">None</code> if the member is <code class="docutils literal notranslate">NULL</code> and
<code class="xref c c-macro docutils literal notranslate">T_OBJECT_EX</code> raises an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>. Try to use
<code class="xref c c-macro docutils literal notranslate">T_OBJECT_EX</code> over <code class="xref c c-macro docutils literal notranslate">T_OBJECT</code> because <code class="xref c c-macro docutils literal notranslate">T_OBJECT_EX</code>
handles use of the <a class="reference internal" href="../reference/simple_stmts.html#del"><code class="xref std std-keyword docutils literal notranslate">del</code></a> statement on that attribute more correctly
than <code class="xref c c-macro docutils literal notranslate">T_OBJECT</code>.
<code class="xref py py-attr docutils literal notranslate">flags</code> can be <code class="docutils literal notranslate">0</code> for write and read access or <code class="xref c c-macro docutils literal notranslate">READONLY</code> for
read-only access. Using <code class="xref c c-macro docutils literal notranslate">T_STRING</code> for <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-attr docutils literal notranslate">type</code></a> implies
<code class="xref c c-macro docutils literal notranslate">READONLY</code>. <code class="xref c c-macro docutils literal notranslate">T_STRING</code> data is interpreted as UTF-8.
Only <code class="xref c c-macro docutils literal notranslate">T_OBJECT</code> and <code class="xref c c-macro docutils literal notranslate">T_OBJECT_EX</code>
members can be deleted. (They are set to <code class="docutils literal notranslate">NULL</code>).
Heap allocated types (created using <a class="reference internal" href="type.html#c.PyType_FromSpec" title="PyType_FromSpec"><code class="xref c c-func docutils literal notranslate">PyType_FromSpec()</code></a> or similar),
<code class="docutils literal notranslate">PyMemberDef</code> may contain definitions for the special members
<code class="docutils literal notranslate">__dictoffset__</code>, <code class="docutils literal notranslate">__weaklistoffset__</code> and <code class="docutils literal notranslate">__vectorcalloffset__</code>,
corresponding to
<a class="reference internal" href="typeobj.html#c.PyTypeObject.tp_dictoffset" title="PyTypeObject.tp_dictoffset"><code class="xref c c-member docutils literal notranslate">tp_dictoffset</code></a>,
<a class="reference internal" href="typeobj.html#c.PyTypeObject.tp_weaklistoffset" title="PyTypeObject.tp_weaklistoffset"><code class="xref c c-member docutils literal notranslate">tp_weaklistoffset</code></a> and
<a class="reference internal" href="typeobj.html#c.PyTypeObject.tp_vectorcall_offset" title="PyTypeObject.tp_vectorcall_offset"><code class="xref c c-member docutils literal notranslate">tp_vectorcall_offset</code></a> in type objects.
These must be defined with <code class="docutils literal notranslate">T_PYSSIZET</code> and <code class="docutils literal notranslate">READONLY</code>, for example:
<div class="highlight-c notranslate"><div class="highlight"><pre>static PyMemberDef spam_type_members[] = {
 {&quot;__dictoffset__&quot;, T_PYSSIZET, offsetof(Spam_object, dict), READONLY},
 {NULL} /* Sentinel */
};
</pre></div>
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyMember_GetOne">
<a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *PyMember_GetOne(const char *obj_addr, struct <a class="reference internal" href="#c.PyMemberDef" title="PyMemberDef">PyMemberDef</a> *m)<a class="headerlink" href="#c.PyMember_GetOne" title="Permalink to this definition">¶</a> </dt>
<dd>Get an attribute belonging to the object at address obj_addr. The
attribute is described by <code class="docutils literal notranslate">PyMemberDef</code> m. Returns <code class="docutils literal notranslate">NULL</code>
on error.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyMember_SetOne">
int PyMember_SetOne(char *obj_addr, struct <a class="reference internal" href="#c.PyMemberDef" title="PyMemberDef">PyMemberDef</a> *m, <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.PyMember_SetOne" title="Permalink to this definition">¶</a> </dt>
<dd>Set an attribute belonging to the object at address obj_addr to object o.
The attribute to set is described by <code class="docutils literal notranslate">PyMemberDef</code> m. Returns <code class="docutils literal notranslate">0</code>
if successful and a negative value on failure.
</dd></dl>

<dl class="c type">
<dt class="sig sig-object c" id="c.PyGetSetDef">
type PyGetSetDef<a class="headerlink" href="#c.PyGetSetDef" title="Permalink to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> (including all members).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">PyTypeObject.tp_getset</code></a> slot.
<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">Field</th>
<th class="head">C Type</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td>name</td>
<td>const char *</td>
<td>attribute name</td>
</tr>
<tr class="row-odd"><td>get</td>
<td>getter</td>
<td>C function to get the attribute</td>
</tr>
<tr class="row-even"><td>set</td>
<td>setter</td>
<td>optional C function to set or
delete the attribute, if omitted
the attribute is readonly</td>
</tr>
<tr class="row-odd"><td>doc</td>
<td>const char *</td>
<td>optional docstring</td>
</tr>
<tr class="row-even"><td>closure</td>
<td>void *</td>
<td>optional function pointer,
providing additional data for
getter and setter</td>
</tr>
</tbody>
</table>
The <code class="docutils literal notranslate">get</code> function takes one <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a>* parameter (the
instance) and a function pointer (the associated <code class="docutils literal notranslate">closure</code>):
<div class="highlight-c notranslate"><div class="highlight"><pre>typedef PyObject *(*getter)(PyObject *, void *);
</pre></div>
</div>
It should return a new reference on success or <code class="docutils literal notranslate">NULL</code> with a set exception
on failure.
<code class="docutils literal notranslate">set</code> functions take two <a class="reference internal" href="#c.PyObject" title="PyObject">PyObject</a>* parameters (the instance and
the value to be set) and a function pointer (the associated <code class="docutils literal notranslate">closure</code>):
<div class="highlight-c notranslate"><div class="highlight"><pre>typedef int (*setter)(PyObject *, PyObject *, void *);
</pre></div>
</div>
In case the attribute should be deleted the second parameter is <code class="docutils literal notranslate">NULL</code>.
Should return <code class="docutils literal notranslate">0</code> on success or <code class="docutils literal notranslate">-1</code> with a set exception on failure.
</dd></dl>

</section>
</section>

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<li><a class="reference internal" href="#implementing-functions-and-methods">Implementing functions and methods</a></li>
<li><a class="reference internal" href="#accessing-attributes-of-extension-types">Accessing attributes of extension types</a></li>
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