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 <section id="reference-counting">
<h1>Reference Counting<a class="headerlink" href="#reference-counting" title="Link to this heading">¶</a></h1>
The functions and macros in this section are used for managing reference counts
of Python objects.
<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(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_REFCNT" title="Link to this definition">¶</a> </dt>
<dd>Get the reference count of the Python object o.
Note that the returned value may not actually reflect how many
references to the object are actually held. For example, some
objects are “immortal” and have a very high refcount that does not
reflect the actual number of references. Consequently, do not rely
on the returned value to be accurate, other than a value of 0 or 1.
Use the <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> function to set an object reference count.
<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.
</div>
<div class="versionchanged">
Changed in version 3.11: The parameter type is no longer const <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>*.
</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="structures.html#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="Link to this definition">¶</a> </dt>
<dd>Set the object o reference counter to refcnt.
Note that this function has no effect on
<a class="reference external" href="https://peps.python.org/pep-0683/">immortal</a>
objects.
<div class="versionadded">
New in version 3.9.
</div>
<div class="versionchanged">
Changed in version 3.12: Immortal objects are not modified.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_INCREF">
void Py_INCREF(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_INCREF" title="Link to this definition">¶</a> </dt>
<dd>Indicate taking a new <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> to object o,
indicating it is in use and should not be destroyed.
This function is usually used to convert a <a class="reference internal" href="../glossary.html#term-borrowed-reference">borrowed reference</a> to a
<a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> in-place. The <a class="reference internal" href="#c.Py_NewRef" title="Py_NewRef"><code class="xref c c-func docutils literal notranslate">Py_NewRef()</code></a> function can be
used to create a new <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a>.
When done using the object, release it by calling <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a>.
The object must not be <code class="docutils literal notranslate">NULL</code>; if you aren’t sure that it isn’t
<code class="docutils literal notranslate">NULL</code>, use <a class="reference internal" href="#c.Py_XINCREF" title="Py_XINCREF"><code class="xref c c-func docutils literal notranslate">Py_XINCREF()</code></a>.
Do not expect this function to actually modify o in any way.
For at least <a class="reference external" href="https://peps.python.org/pep-0683/">some objects</a>,
this function has no effect.
<div class="versionchanged">
Changed in version 3.12: Immortal objects are not modified.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_XINCREF">
void Py_XINCREF(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_XINCREF" title="Link to this definition">¶</a> </dt>
<dd>Similar to <a class="reference internal" href="#c.Py_INCREF" title="Py_INCREF"><code class="xref c c-func docutils literal notranslate">Py_INCREF()</code></a>, but the object o can be <code class="docutils literal notranslate">NULL</code>,
in which case this has no effect.
See also <a class="reference internal" href="#c.Py_XNewRef" title="Py_XNewRef"><code class="xref c c-func docutils literal notranslate">Py_XNewRef()</code></a>.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_NewRef">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *Py_NewRef(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_NewRef" title="Link to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> since version 3.10.Create a new <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> to an object:
call <a class="reference internal" href="#c.Py_INCREF" title="Py_INCREF"><code class="xref c c-func docutils literal notranslate">Py_INCREF()</code></a> on o and return the object o.
When the <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> is no longer needed, <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a>
should be called on it to release the reference.
The object o must not be <code class="docutils literal notranslate">NULL</code>; use <a class="reference internal" href="#c.Py_XNewRef" title="Py_XNewRef"><code class="xref c c-func docutils literal notranslate">Py_XNewRef()</code></a> if o can be
<code class="docutils literal notranslate">NULL</code>.
For example:
<div class="highlight-c notranslate"><div class="highlight"><pre>Py_INCREF(obj);
self-&gt;attr = obj;
</pre></div>
</div>
can be written as:
<div class="highlight-c notranslate"><div class="highlight"><pre>self-&gt;attr = Py_NewRef(obj);
</pre></div>
</div>
See also <a class="reference internal" href="#c.Py_INCREF" title="Py_INCREF"><code class="xref c c-func docutils literal notranslate">Py_INCREF()</code></a>.
<div class="versionadded">
New in version 3.10.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_XNewRef">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *Py_XNewRef(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_XNewRef" title="Link to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a> since version 3.10.Similar to <a class="reference internal" href="#c.Py_NewRef" title="Py_NewRef"><code class="xref c c-func docutils literal notranslate">Py_NewRef()</code></a>, but the object o can be NULL.
If the object o is <code class="docutils literal notranslate">NULL</code>, the function just returns <code class="docutils literal notranslate">NULL</code>.
<div class="versionadded">
New in version 3.10.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_DECREF">
void Py_DECREF(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_DECREF" title="Link to this definition">¶</a> </dt>
<dd>Release a <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> to object o, indicating the
reference is no longer used.
Once the last <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> is released
(i.e. the object’s reference count reaches 0),
the object’s type’s deallocation
function (which must not be <code class="docutils literal notranslate">NULL</code>) is invoked.
This function is usually used to delete a <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> before
exiting its scope.
The object must not be <code class="docutils literal notranslate">NULL</code>; if you aren’t sure that it isn’t <code class="docutils literal notranslate">NULL</code>,
use <a class="reference internal" href="#c.Py_XDECREF" title="Py_XDECREF"><code class="xref c c-func docutils literal notranslate">Py_XDECREF()</code></a>.
Do not expect this function to actually modify o in any way.
For at least <a class="reference external" href="https://peps.python.org/pep-0683/">some objects</a>,
this function has no effect.
<div class="admonition warning">
Warning
The deallocation function can cause arbitrary Python code to be invoked (e.g.
when a class instance with a <a class="reference internal" href="../reference/datamodel.html#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> method is deallocated). While
exceptions in such code are not propagated, the executed code has free access to
all Python global variables. This means that any object that is reachable from
a global variable should be in a consistent state before <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a> is
invoked. For example, code to delete an object from a list should copy a
reference to the deleted object in a temporary variable, update the list data
structure, and then call <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a> for the temporary variable.
</div>
<div class="versionchanged">
Changed in version 3.12: Immortal objects are not modified.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_XDECREF">
void Py_XDECREF(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_XDECREF" title="Link to this definition">¶</a> </dt>
<dd>Similar to <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a>, but the object o can be <code class="docutils literal notranslate">NULL</code>,
in which case this has no effect.
The same warning from <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a> applies here as well.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_CLEAR">
void Py_CLEAR(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_CLEAR" title="Link to this definition">¶</a> </dt>
<dd>Release a <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> for object o.
The object may be <code class="docutils literal notranslate">NULL</code>, in
which case the macro has no effect; otherwise the effect is the same as for
<a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a>, except that the argument is also set to <code class="docutils literal notranslate">NULL</code>. The warning
for <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a> does not apply with respect to the object passed because
the macro carefully uses a temporary variable and sets the argument to <code class="docutils literal notranslate">NULL</code>
before releasing the reference.
It is a good idea to use this macro whenever releasing a reference
to an object that might be traversed during garbage collection.
<div class="versionchanged">
Changed in version 3.12: The macro argument is now only evaluated once. If the argument has side
effects, these are no longer duplicated.
</div>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_IncRef">
void Py_IncRef(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_IncRef" title="Link to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a>.Indicate taking a new <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> to object o.
A function version of <a class="reference internal" href="#c.Py_XINCREF" title="Py_XINCREF"><code class="xref c c-func docutils literal notranslate">Py_XINCREF()</code></a>.
It can be used for runtime dynamic embedding of Python.
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.Py_DecRef">
void Py_DecRef(<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *o)<a class="headerlink" href="#c.Py_DecRef" title="Link to this definition">¶</a> </dt>
<dd> Part of the <a class="reference internal" href="stable.html#stable">Stable ABI</a>.Release a <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> to object o.
A function version of <a class="reference internal" href="#c.Py_XDECREF" title="Py_XDECREF"><code class="xref c c-func docutils literal notranslate">Py_XDECREF()</code></a>.
It can be used for runtime dynamic embedding of Python.
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_SETREF">
Py_SETREF(dst, src)<a class="headerlink" href="#c.Py_SETREF" title="Link to this definition">¶</a> </dt>
<dd>Macro safely releasing a <a class="reference internal" href="../glossary.html#term-strong-reference">strong reference</a> to object dst
and setting dst to src.
As in case of <a class="reference internal" href="#c.Py_CLEAR" title="Py_CLEAR"><code class="xref c c-func docutils literal notranslate">Py_CLEAR()</code></a>, “the obvious” code can be deadly:
<div class="highlight-c notranslate"><div class="highlight"><pre>Py_DECREF(dst);
dst = src;
</pre></div>
</div>
The safe way is:
<div class="highlight-c notranslate"><div class="highlight"><pre>Py_SETREF(dst, src);
</pre></div>
</div>
That arranges to set dst to src _before_ releasing the reference
to the old value of dst, so that any code triggered as a side-effect
of dst getting torn down no longer believes dst points
to a valid object.
<div class="versionadded">
New in version 3.6.
</div>
<div class="versionchanged">
Changed in version 3.12: The macro arguments are now only evaluated once. If an argument has side
effects, these are no longer duplicated.
</div>
</dd></dl>

<dl class="c macro">
<dt class="sig sig-object c" id="c.Py_XSETREF">
Py_XSETREF(dst, src)<a class="headerlink" href="#c.Py_XSETREF" title="Link to this definition">¶</a> </dt>
<dd>Variant of <a class="reference internal" href="#c.Py_SETREF" title="Py_SETREF"><code class="xref c c-macro docutils literal notranslate">Py_SETREF</code></a> macro that uses <a class="reference internal" href="#c.Py_XDECREF" title="Py_XDECREF"><code class="xref c c-func docutils literal notranslate">Py_XDECREF()</code></a> instead
of <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a>.
<div class="versionadded">
New in version 3.6.
</div>
<div class="versionchanged">
Changed in version 3.12: The macro arguments are now only evaluated once. If an argument has side
effects, these are no longer duplicated.
</div>
</dd></dl>

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