pythongh-98154: Clarify Usage of "Reference Count" In the Docs (pytho…

…ngh-107552)

PEP 683 (immortal objects) revealed some ways in which the Python documentation has been unnecessarily coupled to the implementation details of reference counts.  In the end users should focus on reference ownership, including taking references and releasing them, rather than on how many reference counts an object has.

This change updates the documentation to reflect that perspective.  It also updates the docs relative to immortal objects in a handful of places.

Doc/c-api/allocation.rst

@@ -29,12 +29,13 @@ Allocating Objects on the Heap
 
 .. c:macro:: PyObject_New(TYPE, typeobj)
 
-   Allocate a new Python object using the C structure type *TYPE* and the
-   Python type object *typeobj* (``PyTypeObject*``).
-   Fields not defined by the Python object header
-   are not initialized; the object's reference count will be one.  The size of
-   the memory allocation is determined from the :c:member:`~PyTypeObject.tp_basicsize` field of
-   the type object.
+   Allocate a new Python object using the C structure type *TYPE*
+   and the Python type object *typeobj* (``PyTypeObject*``).
+   Fields not defined by the Python object header are not initialized.
+   The caller will own the only reference to the object
+   (i.e. its reference count will be one).
+   The size of the memory allocation is determined from the
+   :c:member:`~PyTypeObject.tp_basicsize` field of the type object.
 
 
 .. c:macro:: PyObject_NewVar(TYPE, typeobj, size)

Doc/c-api/arg.rst

@@ -293,8 +293,10 @@ Other objects
 
 ``O`` (object) [PyObject \*]
    Store a Python object (without any conversion) in a C object pointer.  The C
-   program thus receives the actual object that was passed.  The object's reference
-   count is not increased.  The pointer stored is not ``NULL``.
+   program thus receives the actual object that was passed.  A new
+   :term:`strong reference` to the object is not created
+   (i.e. its reference count is not increased).
+   The pointer stored is not ``NULL``.
 
 ``O!`` (object) [*typeobject*, PyObject \*]
    Store a Python object in a C object pointer.  This is similar to ``O``, but
@@ -378,7 +380,8 @@ inside nested parentheses.  They are:
    mutually exclude each other.
 
 Note that any Python object references which are provided to the caller are
-*borrowed* references; do not decrement their reference count!
+*borrowed* references; do not release them
+(i.e. do not decrement their reference count)!
 
 Additional arguments passed to these functions must be addresses of variables
 whose type is determined by the format string; these are used to store values
@@ -621,8 +624,10 @@ Building values
       Convert a C :c:type:`Py_complex` structure to a Python complex number.
 
    ``O`` (object) [PyObject \*]
-      Pass a Python object untouched (except for its reference count, which is
-      incremented by one).  If the object passed in is a ``NULL`` pointer, it is assumed
+      Pass a Python object untouched but create a new
+      :term:`strong reference` to it
+      (i.e. its reference count is incremented by one).
+      If the object passed in is a ``NULL`` pointer, it is assumed
       that this was caused because the call producing the argument found an error and
       set an exception. Therefore, :c:func:`Py_BuildValue` will return ``NULL`` but won't
       raise an exception.  If no exception has been raised yet, :exc:`SystemError` is
@@ -632,7 +637,7 @@ Building values
       Same as ``O``.
 
    ``N`` (object) [PyObject \*]
-      Same as ``O``, except it doesn't increment the reference count on the object.
+      Same as ``O``, except it doesn't create a new :term:`strong reference`.
       Useful when the object is created by a call to an object constructor in the
       argument list.
 

Doc/c-api/buffer.rst

@@ -102,7 +102,9 @@ a buffer, see :c:func:`PyObject_GetBuffer`.
    .. c:member:: PyObject *obj
 
       A new reference to the exporting object. The reference is owned by
-      the consumer and automatically decremented and set to ``NULL`` by
+      the consumer and automatically released
+      (i.e. reference count decremented)
+      and set to ``NULL`` by
       :c:func:`PyBuffer_Release`. The field is the equivalent of the return
       value of any standard C-API function.
 
@@ -454,7 +456,8 @@ Buffer-related functions
 
 .. c:function:: void PyBuffer_Release(Py_buffer *view)
 
-   Release the buffer *view* and decrement the reference count for
+   Release the buffer *view* and release the :term:`strong reference`
+   (i.e. decrement the reference count) to the view's supporting object,
    ``view->obj``. This function MUST be called when the buffer
    is no longer being used, otherwise reference leaks may occur.
 

Doc/c-api/bytes.rst

@@ -184,8 +184,8 @@ called with a non-bytes parameter.
 .. c:function:: void PyBytes_ConcatAndDel(PyObject **bytes, PyObject *newpart)
 
    Create a new bytes object in *\*bytes* containing the contents of *newpart*
-   appended to *bytes*.  This version decrements the reference count of
-   *newpart*.
+   appended to *bytes*.  This version releases the :term:`strong reference`
+   to *newpart* (i.e. decrements its reference count).
 
 
 .. c:function:: int _PyBytes_Resize(PyObject **bytes, Py_ssize_t newsize)

Doc/c-api/exceptions.rst

@@ -110,7 +110,8 @@ For convenience, some of these functions will always return a
 
    This is the most common way to set the error indicator.  The first argument
    specifies the exception type; it is normally one of the standard exceptions,
-   e.g. :c:data:`PyExc_RuntimeError`.  You need not increment its reference count.
+   e.g. :c:data:`PyExc_RuntimeError`.  You need not create a new
+   :term:`strong reference` to it (e.g. with :c:func:`Py_INCREF`).
    The second argument is an error message; it is decoded from ``'utf-8'``.
 
 

Doc/c-api/init_config.rst

@@ -1128,7 +1128,7 @@ PyConfig
 
    .. c:member:: int show_ref_count
 
-      Show total reference count at exit?
+      Show total reference count at exit (excluding immortal objects)?
 
       Set to ``1`` by :option:`-X showrefcount <-X>` command line option.
 

Doc/c-api/intro.rst

@@ -287,60 +287,67 @@ true if (and only if) the object pointed to by *a* is a Python list.
 Reference Counts
 ----------------
 
-The reference count is important because today's computers have a  finite (and
-often severely limited) memory size; it counts how many  different places there
-are that have a reference to an object.  Such a  place could be another object,
-or a global (or static) C variable, or  a local variable in some C function.
-When an object's reference count  becomes zero, the object is deallocated.  If
-it contains references to  other objects, their reference count is decremented.
-Those other  objects may be deallocated in turn, if this decrement makes their
-reference count become zero, and so on.  (There's an obvious problem  with
-objects that reference each other here; for now, the solution is  "don't do
-that.")
+The reference count is important because today's computers have a  finite
+(and often severely limited) memory size; it counts how many different
+places there are that have a :term:`strong reference` to an object.
+Such a place could be another object, or a global (or static) C variable,
+or a local variable in some C function.
+When the last :term:`strong reference` to an object is released
+(i.e. its reference count becomes zero), the object is deallocated.
+If it contains references to other objects, those references are released.
+Those other objects may be deallocated in turn, if there are no more
+references to them, and so on.  (There's an obvious problem  with
+objects that reference each other here; for now, the solution
+is "don't do that.")
 
 .. index::
    single: Py_INCREF()
    single: Py_DECREF()
 
-Reference counts are always manipulated explicitly.  The normal way is  to use
-the macro :c:func:`Py_INCREF` to increment an object's reference count by one,
-and :c:func:`Py_DECREF` to decrement it by   one.  The :c:func:`Py_DECREF` macro
+Reference counts are always manipulated explicitly.  The normal way is
+to use the macro :c:func:`Py_INCREF` to take a new reference to an
+object (i.e. increment its reference count by one),
+and :c:func:`Py_DECREF` to release that reference (i.e. decrement the
+reference count by one).  The :c:func:`Py_DECREF` macro
 is considerably more complex than the incref one, since it must check whether
 the reference count becomes zero and then cause the object's deallocator to be
-called. The deallocator is a function pointer contained in the object's type
-structure.  The type-specific deallocator takes care of decrementing the
-reference counts for other objects contained in the object if this is a compound
+called.  The deallocator is a function pointer contained in the object's type
+structure.  The type-specific deallocator takes care of releasing references
+for other objects contained in the object if this is a compound
 object type, such as a list, as well as performing any additional finalization
 that's needed.  There's no chance that the reference count can overflow; at
 least as many bits are used to hold the reference count as there are distinct
 memory locations in virtual memory (assuming ``sizeof(Py_ssize_t) >= sizeof(void*)``).
 Thus, the reference count increment is a simple operation.
 
-It is not necessary to increment an object's reference count for every  local
-variable that contains a pointer to an object.  In theory, the  object's
+It is not necessary to hold a :term:`strong reference` (i.e. increment
+the reference count) for every local variable that contains a pointer
+to an object.  In theory, the  object's
 reference count goes up by one when the variable is made to  point to it and it
 goes down by one when the variable goes out of  scope.  However, these two
 cancel each other out, so at the end the  reference count hasn't changed.  The
 only real reason to use the  reference count is to prevent the object from being
 deallocated as  long as our variable is pointing to it.  If we know that there
 is at  least one other reference to the object that lives at least as long as
-our variable, there is no need to increment the reference count  temporarily.
+our variable, there is no need to take a new :term:`strong reference`
+(i.e. increment the reference count) temporarily.
 An important situation where this arises is in objects  that are passed as
 arguments to C functions in an extension module  that are called from Python;
 the call mechanism guarantees to hold a  reference to every argument for the
 duration of the call.
 
 However, a common pitfall is to extract an object from a list and hold on to it
-for a while without incrementing its reference count. Some other operation might
-conceivably remove the object from the list, decrementing its reference count
+for a while without taking a new reference.  Some other operation might
+conceivably remove the object from the list, releasing that reference,
 and possibly deallocating it. The real danger is that innocent-looking
 operations may invoke arbitrary Python code which could do this; there is a code
 path which allows control to flow back to the user from a :c:func:`Py_DECREF`, so
 almost any operation is potentially dangerous.
 
 A safe approach is to always use the generic operations (functions  whose name
 begins with ``PyObject_``, ``PyNumber_``, ``PySequence_`` or ``PyMapping_``).
-These operations always increment the reference count of the object they return.
+These operations always create a new :term:`strong reference`
+(i.e. increment the reference count) of the object they return.
 This leaves the caller with the responsibility to call :c:func:`Py_DECREF` when
 they are done with the result; this soon becomes second nature.
 
@@ -356,7 +363,7 @@ to objects (objects are not owned: they are always shared).  "Owning a
 reference" means being responsible for calling Py_DECREF on it when the
 reference is no longer needed.  Ownership can also be transferred, meaning that
 the code that receives ownership of the reference then becomes responsible for
-eventually decref'ing it by calling :c:func:`Py_DECREF` or :c:func:`Py_XDECREF`
+eventually releasing it by calling :c:func:`Py_DECREF` or :c:func:`Py_XDECREF`
 when it's no longer needed---or passing on this responsibility (usually to its
 caller). When a function passes ownership of a reference on to its caller, the
 caller is said to receive a *new* reference.  When no ownership is transferred,
@@ -414,9 +421,9 @@ For example, the above two blocks of code could be replaced by the following
 
 It is much more common to use :c:func:`PyObject_SetItem` and friends with items
 whose references you are only borrowing, like arguments that were passed in to
-the function you are writing.  In that case, their behaviour regarding reference
-counts is much saner, since you don't have to increment a reference count so you
-can give a reference away ("have it be stolen").  For example, this function
+the function you are writing.  In that case, their behaviour regarding references
+is much saner, since you don't have to take a new reference just so you
+can give that reference away ("have it be stolen").  For example, this function
 sets all items of a list (actually, any mutable sequence) to a given item::
 
    int

Doc/c-api/module.rst

@@ -546,7 +546,7 @@ state:
    .. note::
 
       Unlike other functions that steal references, ``PyModule_AddObject()``
-      only decrements the reference count of *value* **on success**.
+      only releases the reference to *value* **on success**.
 
       This means that its return value must be checked, and calling code must
       :c:func:`Py_XDECREF` *value* manually on error.

Doc/c-api/object.rst

@@ -15,8 +15,8 @@ Object Protocol
 .. c:macro:: Py_RETURN_NOTIMPLEMENTED
 
    Properly handle returning :c:data:`Py_NotImplemented` from within a C
-   function (that is, increment the reference count of NotImplemented and
-   return it).
+   function (that is, create a new :term:`strong reference`
+   to NotImplemented and return it).
 
 
 .. c:function:: int PyObject_Print(PyObject *o, FILE *fp, int flags)
@@ -357,11 +357,12 @@ Object Protocol
 
    When *o* is non-``NULL``, returns a type object corresponding to the object type
    of object *o*. On failure, raises :exc:`SystemError` and returns ``NULL``.  This
-   is equivalent to the Python expression ``type(o)``. This function increments the
-   reference count of the return value. There's really no reason to use this
+   is equivalent to the Python expression ``type(o)``.
+   This function creates a new :term:`strong reference` to the return value.
+   There's really no reason to use this
    function instead of the :c:func:`Py_TYPE()` function, which returns a
-   pointer of type :c:expr:`PyTypeObject*`, except when the incremented reference
-   count is needed.
+   pointer of type :c:expr:`PyTypeObject*`, except when a new
+   :term:`strong reference` is needed.
 
 
 .. c:function:: int PyObject_TypeCheck(PyObject *o, PyTypeObject *type)