May 3, 2024 · Feb 29, 2024 · Feb 29, 2024 · Feb 29, 2024 · Feb 29, 2024 · Mar 1, 2024
diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
 :ref:`Type parameters <type-params>` can exist on classes, functions, and type
 aliases.

 .. class:: TypeVar(name, bound)
 .. class:: TypeVar(name, bound, default_value)

   A :class:`typing.TypeVar`. ``name`` is the name of the type variable.
   ``bound`` is the bound or constraints, if any. If ``bound`` is a :class:`Tuple`,
   it represents constraints; otherwise it represents the bound.
   A :class:`typing.TypeVar`. *name* is the name of the type variable.
   *bound* is the bound or constraints, if any. If *bound* is a :class:`Tuple`,
   it represents constraints; otherwise it represents the bound. *default_value*
   is the default value, if any.

   .. doctest::

        >>> print(ast.dump(ast.parse("type Alias[T: int] = list[T]"), indent=4))
        >>> print(ast.dump(ast.parse("type Alias[T: int = bool] = list[T]"), indent=4))
        Module(
            body=[
                TypeAlias(
                    name=Name(id='Alias', ctx=Store()),
                    type_params=[
                        TypeVar(
                            name='T',
                            bound=Name(id='int', ctx=Load()))],
                            bound=Name(id='int', ctx=Load()),
                            default_value=Name(id='bool', ctx=Load()))],
                    value=Subscript(
                        value=Name(id='list', ctx=Load()),
                        slice=Name(id='T', ctx=Load()),

   .. versionadded:: 3.12

 .. class:: ParamSpec(name)
   .. versionchanged:: 3.13
      Added the *default_value* parameter.

 .. class:: ParamSpec(name, default_value)

   A :class:`typing.ParamSpec`. ``name`` is the name of the parameter specification.
   A :class:`typing.ParamSpec`. *name* is the name of the parameter specification.
   *default_value* is the default value, if any.

   .. doctest::

        >>> print(ast.dump(ast.parse("type Alias[**P] = Callable[P, int]"), indent=4))
        >>> print(ast.dump(ast.parse("type Alias[**P = (int, str)] = Callable[P, int]"), indent=4))
        Module(
            body=[
                TypeAlias(
                    name=Name(id='Alias', ctx=Store()),
                    type_params=[
                        ParamSpec(name='P')],
                        ParamSpec(
                            name='P',
                            default_value=Tuple(
                                elts=[
                                    Name(id='int', ctx=Load()),
                                    Name(id='str', ctx=Load())],
                                ctx=Load()))],
                    value=Subscript(
                        value=Name(id='Callable', ctx=Load()),
                        slice=Tuple(

   .. versionadded:: 3.12

 .. class:: TypeVarTuple(name)
   .. versionchanged:: 3.13
      Added the *default_value* parameter.

 .. class:: TypeVarTuple(name, default_value)

   A :class:`typing.TypeVarTuple`. ``name`` is the name of the type variable tuple.
   A :class:`typing.TypeVarTuple`. *name* is the name of the type variable tuple.
   *default_value* is the default value, if any.

   .. doctest::

        >>> print(ast.dump(ast.parse("type Alias[*Ts] = tuple[*Ts]"), indent=4))
        >>> print(ast.dump(ast.parse("type Alias[*Ts = ()] = tuple[*Ts]"), indent=4))
        Module(
            body=[
                TypeAlias(
                    name=Name(id='Alias', ctx=Store()),
                    type_params=[
                        TypeVarTuple(name='Ts')],
                        TypeVarTuple(
                            name='Ts',
                            default_value=Tuple(elts=[], ctx=Load()))],
                    value=Subscript(
                        value=Name(id='tuple', ctx=Load()),
                        slice=Tuple(

   .. versionadded:: 3.12

   .. versionchanged:: 3.13
      Added the *default_value* parameter.

 Function and class definitions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst

 .. _typevar:

 .. class:: TypeVar(name, *constraints, bound=None, covariant=False, contravariant=False, infer_variance=False)
 .. class:: TypeVar(name, *constraints, bound=None, covariant=False, contravariant=False, infer_variance=False, default=<unrepresentable>)

   Type variable.

         the constraints are evaluated only when the attribute is accessed, not when
         the type variable is created (see :ref:`lazy-evaluation`).

   .. attribute:: __default__

      The default value of the type variable, if any. This attribute is ``None``
      if the type variable has no default, and :class:`types.NoneType`
      if the default is set to ``None``.

      .. versionadded:: 3.13

   .. versionchanged:: 3.12

      Type variables can now be declared using the
      :ref:`type parameter <type-params>` syntax introduced by :pep:`695`.
      The ``infer_variance`` parameter was added.

   .. versionchanged:: 3.13

      Support for default values was added.

 .. _typevartuple:

 .. class:: TypeVarTuple(name)
 .. class:: TypeVarTuple(name, default=<unrepresentable>)

   Type variable tuple. A specialized form of :ref:`type variable <typevar>`
   that enables *variadic* generics.

      The name of the type variable tuple.

   .. attribute:: __default__

      The default value of the type variable tuple, if any. This attribute is ``None``
      if the type variable tuple has no default, and :class:`types.NoneType`
      if the default is set to ``None``.

      .. versionadded:: 3.13

   .. versionadded:: 3.11

   .. versionchanged:: 3.12

      Type variable tuples can now be declared using the
      :ref:`type parameter <type-params>` syntax introduced by :pep:`695`.

 .. class:: ParamSpec(name, *, bound=None, covariant=False, contravariant=False)
   .. versionchanged:: 3.13

      Support for default values was added.

 .. class:: ParamSpec(name, *, bound=None, covariant=False, contravariant=False, default=<unrepresentable>)

   Parameter specification variable.  A specialized version of
   :ref:`type variables <typevar>`.

      The name of the parameter specification.

   .. attribute:: __default__

      The default value of the parameter specification, if any. This attribute is ``None``
      if the parameter specification has no default, and :class:`types.NoneType`
      if the default is set to ``None``.

      .. versionadded:: 3.13

   Parameter specification variables created with ``covariant=True`` or
   ``contravariant=True`` can be used to declare covariant or contravariant
   generic types.  The ``bound`` argument is also accepted, similar to
      Parameter specifications can now be declared using the
      :ref:`type parameter <type-params>` syntax introduced by :pep:`695`.

   .. versionchanged:: 3.13

      Support for default values was added.

   .. note::
      Only parameter specification variables defined in global scope can
      be pickled.
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst

 .. versionadded:: 3.12

 .. versionchanged:: 3.13
   Support for default values was added (see :pep:`696`).

 .. index::
   single: type parameters

 .. productionlist:: python-grammar
   type_params: "[" `type_param` ("," `type_param`)* "]"
   type_param: `typevar` | `typevartuple` | `paramspec`
   typevar: `identifier` (":" `expression`)?
   typevartuple: "*" `identifier`
   paramspec: "**" `identifier`
   typevar: `identifier` (":" `expression`)? ("=" `expression`)?
   typevartuple: "*" `identifier` ("=" `expression`)?
   paramspec: "**" `identifier` ("=" `expression`)?

 :ref:`Functions <def>` (including :ref:`coroutines <async def>`),
 :ref:`classes <class>` and :ref:`type aliases <type>` may
 :data:`typing.TypeVarTuple`\ s and :data:`typing.ParamSpec`\ s cannot have bounds
 or constraints.

 All three flavors of type parameters can also have a *default value*, which is used
 when the type parameter is not explicitly provided. This is added by appending
 a single equals sign (``=``) followed by an expression. Like the bounds and
 constraints of type variables, the default value is not evaluated when the
 object is created, but only when the type parameter's ``__default__`` attribute
 is accessed. To this end, the default value is evaluated in a separate
 :ref:`annotation scope <annotation-scopes>`.

 The following example indicates the full set of allowed type parameter declarations::

   def overly_generic[
      SimpleTypeVar,
      TypeVarWithDefault = int,
      TypeVarWithBound: int,
      TypeVarWithConstraints: (str, bytes),
      *SimpleTypeVarTuple,
      **SimpleParamSpec,
      *SimpleTypeVarTuple = (int, float),
      **SimpleParamSpec = (str, bytearray),
   ](
      a: SimpleTypeVar,
      b: TypeVarWithBound,
      c: Callable[SimpleParamSpec, TypeVarWithConstraints],
      *d: SimpleTypeVarTuple,
      b: TypeVarWithDefault,
      c: TypeVarWithBound,
      d: Callable[SimpleParamSpec, TypeVarWithConstraints],
      *e: SimpleTypeVarTuple,
   ): ...

 .. _generic-functions:
diff --git a/Doc/reference/executionmodel.rst b/Doc/reference/executionmodel.rst
 * Type parameter lists for :ref:`generic classes <generic-classes>`.
  A generic class's base classes and
  keyword arguments are executed within the annotation scope, but its decorators are not.
 * The boundsandconstraintsfor typevariables
 * The bounds, constraints,anddefault valuesfor typeparameters
  (:ref:`lazily evaluated <lazy-evaluation>`).
 * The value of type aliases (:ref:`lazily evaluated <lazy-evaluation>`).

 .. versionadded:: 3.12
   Annotation scopes were introduced in Python 3.12 as part of :pep:`695`.

 .. versionchanged:: 3.13
   Annotation scopes are now also used for type parameter defaults, as
   introduced by :pep:`696`.

 .. _lazy-evaluation:

 Lazy evaluation
 ---------------

 The values of type aliases created through the :keyword:`type` statement are
 *lazily evaluated*. The same applies to the boundsandconstraints of type
 *lazily evaluated*. The same applies to the bounds, constraints,anddefault values of type
 variables created through the :ref:`type parameter syntax <type-params>`.
 This means that they are not evaluated when the type alias or type variable is
 created. Instead, they are only evaluated when doing so is necessary to resolve
diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst

 New typing features:

 * :pep:`696`: Type parameters (:data:`typing.TypeVar`, :data:`typing.ParamSpec`,
  and :data:`typing.TypeVarTuple`) now support defaults.
 * :pep:`742`: :data:`typing.TypeIs` was added, providing more intuitive
  type narrowing behavior.

diff --git a/Grammar/python.gram b/Grammar/python.gram
 type_param_seq[asdl_type_param_seq*]: a[asdl_type_param_seq*]=','.type_param+ [','] { a }

 type_param[type_param_ty] (memo):
    | a=NAME b=[type_param_bound] { _PyAST_TypeVar(a->v.Name.id, b, EXTRA) }
    | a=NAME b=[type_param_bound]c=[type_param_default]{ _PyAST_TypeVar(a->v.Name.id, b, c, EXTRA) }
    | '*' a=NAME colon=':' e=expression {
            RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
                ? "cannot use constraints with TypeVarTuple"
                : "cannot use bound with TypeVarTuple")
        }
    | '*' a=NAME { _PyAST_TypeVarTuple(a->v.Name.id, EXTRA) }
    | '*' a=NAMEb=[type_param_starred_default]{ _PyAST_TypeVarTuple(a->v.Name.id, b, EXTRA) }
    | '**' a=NAME colon=':' e=expression {
            RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
                ? "cannot use constraints with ParamSpec"
                : "cannot use bound with ParamSpec")
        }
    | '**' a=NAME { _PyAST_ParamSpec(a->v.Name.id, EXTRA) }
    | '**' a=NAMEb=[type_param_default]{ _PyAST_ParamSpec(a->v.Name.id, b, EXTRA) }

 type_param_bound[expr_ty]: ':' e=expression { e }
 type_param_default[expr_ty]: '=' e=expression {
    CHECK_VERSION(expr_ty, 13, "Type parameter defaults are", e) }
 type_param_starred_default[expr_ty]: '=' e=star_expression {
    CHECK_VERSION(expr_ty, 13, "Type parameter defaults are", e) }

 # EXPRESSIONS
 # -----------
diff --git a/Include/internal/pycore_ast.h b/Include/internal/pycore_ast.h
diff --git a/Include/internal/pycore_ast_state.h b/Include/internal/pycore_ast_state.h
diff --git a/Include/internal/pycore_intrinsics.h b/Include/internal/pycore_intrinsics.h
 #define INTRINSIC_TYPEVAR_WITH_BOUND             2
 #define INTRINSIC_TYPEVAR_WITH_CONSTRAINTS       3
 #define INTRINSIC_SET_FUNCTION_TYPE_PARAMS       4
 #define INTRINSIC_SET_TYPEPARAM_DEFAULT          5

 #define MAX_INTRINSIC_24
 #define MAX_INTRINSIC_25

 typedef PyObject *(*intrinsic_func1)(PyThreadState* tstate, PyObject *value);
 typedef PyObject *(*intrinsic_func2)(PyThreadState* tstate, PyObject *value1, PyObject *value2);
diff --git a/Include/internal/pycore_typevarobject.h b/Include/internal/pycore_typevarobject.h
 extern PyObject *_Py_make_typevartuple(PyThreadState *, PyObject *);
 extern PyObject *_Py_make_typealias(PyThreadState *, PyObject *);
 extern PyObject *_Py_subscript_generic(PyThreadState *, PyObject *);
 extern PyObject *_Py_set_typeparam_default(PyThreadState *, PyObject *, PyObject *);
 extern int _Py_initialize_generic(PyInterpreterState *);
 extern void _Py_clear_generic_types(PyInterpreterState *);
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1798,23 +1798,25 @@ Type parameters
		:ref:`Type parameters <type-params>` can exist on classes, functions, and type
		aliases.

		.. class:: TypeVar(name, bound)
		.. class:: TypeVar(name, bound, default_value)

		A :class:`typing.TypeVar`. ``name`` is the name of the type variable.
		``bound`` is the bound or constraints, if any. If ``bound`` is a :class:`Tuple`,
		it represents constraints; otherwise it represents the bound.
		A :class:`typing.TypeVar`. name is the name of the type variable.
		bound is the bound or constraints, if any. If bound is a :class:`Tuple`,
		it represents constraints; otherwise it represents the bound. default_value
		is the default value, if any.
JelleZijlstra marked this conversation as resolved. OutdatedShow resolvedHide resolved

		.. doctest::

		>>> print(ast.dump(ast.parse("type Alias[T: int] = list[T]"), indent=4))
		>>> print(ast.dump(ast.parse("type Alias[T: int = bool] = list[T]"), indent=4))
		Module(
		body=[
		TypeAlias(
		name=Name(id='Alias', ctx=Store()),
		type_params=[
		TypeVar(
		name='T',
		bound=Name(id='int', ctx=Load()))],
		bound=Name(id='int', ctx=Load()),
		default_value=Name(id='bool', ctx=Load()))],
		value=Subscript(
		value=Name(id='list', ctx=Load()),
		slice=Name(id='T', ctx=Load()),
Expand All		@@ -1823,19 +1825,29 @@ aliases.

		.. versionadded:: 3.12

		.. class:: ParamSpec(name)
		.. versionchanged:: 3.13
		Added the default_value parameter.

		.. class:: ParamSpec(name, default_value)

		A :class:`typing.ParamSpec`. ``name`` is the name of the parameter specification.
		A :class:`typing.ParamSpec`. name is the name of the parameter specification.
		default_value is the default value, if any.
JelleZijlstra marked this conversation as resolved. OutdatedShow resolvedHide resolved

		.. doctest::

		>>> print(ast.dump(ast.parse("type Alias[**P] = Callable[P, int]"), indent=4))
		>>> print(ast.dump(ast.parse("type Alias[**P = (int, str)] = Callable[P, int]"), indent=4))
		Module(
		body=[
		TypeAlias(
		name=Name(id='Alias', ctx=Store()),
		type_params=[
		ParamSpec(name='P')],
		ParamSpec(
		name='P',
		default_value=Tuple(
		elts=[
		Name(id='int', ctx=Load()),
		Name(id='str', ctx=Load())],
		ctx=Load()))],
		value=Subscript(
		value=Name(id='Callable', ctx=Load()),
		slice=Tuple(
Expand All		@@ -1848,19 +1860,25 @@ aliases.

		.. versionadded:: 3.12

		.. class:: TypeVarTuple(name)
		.. versionchanged:: 3.13
		Added the default_value parameter.

		.. class:: TypeVarTuple(name, default_value)

		A :class:`typing.TypeVarTuple`. ``name`` is the name of the type variable tuple.
		A :class:`typing.TypeVarTuple`. name is the name of the type variable tuple.
		default_value is the default value, if any.
JelleZijlstra marked this conversation as resolved. OutdatedShow resolvedHide resolved

		.. doctest::

		>>> print(ast.dump(ast.parse("type Alias[Ts] = tuple[Ts]"), indent=4))
		>>> print(ast.dump(ast.parse("type Alias[Ts = ()] = tuple[Ts]"), indent=4))
		Module(
		body=[
		TypeAlias(
		name=Name(id='Alias', ctx=Store()),
		type_params=[
		TypeVarTuple(name='Ts')],
		TypeVarTuple(
		name='Ts',
		default_value=Tuple(elts=[], ctx=Load()))],
		value=Subscript(
		value=Name(id='tuple', ctx=Load()),
		slice=Tuple(
Expand All		@@ -1874,6 +1892,9 @@ aliases.

		.. versionadded:: 3.12

		.. versionchanged:: 3.13
		Added the default_value parameter.

		Function and class definitions
		^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1616,7 +1616,7 @@ without the dedicated syntax, as documented below.

		.. _typevar:

		.. class:: TypeVar(name, *constraints, bound=None, covariant=False, contravariant=False, infer_variance=False)
		.. class:: TypeVar(name, *constraints, bound=None, covariant=False, contravariant=False, infer_variance=False, default=<unrepresentable>)
JelleZijlstra marked this conversation as resolved. OutdatedShow resolvedHide resolved

		Type variable.

Expand DownExpand Up		@@ -1754,15 +1754,27 @@ without the dedicated syntax, as documented below.
		the constraints are evaluated only when the attribute is accessed, not when
		the type variable is created (see :ref:`lazy-evaluation`).

		.. attribute:: __default__

		The default value of the type variable, if any. This attribute is ``None``
JelleZijlstra marked this conversation as resolved. OutdatedShow resolvedHide resolved AlexWaygood marked this conversation as resolved. OutdatedShow resolvedHide resolved
		if the type variable has no default, and :class:`types.NoneType`
		if the default is set to ``None``.

		.. versionadded:: 3.13

		.. versionchanged:: 3.12

		Type variables can now be declared using the
		:ref:`type parameter <type-params>` syntax introduced by :pep:`695`.
		The ``infer_variance`` parameter was added.

		.. versionchanged:: 3.13

		Support for default values was added.

		.. _typevartuple:

		.. class:: TypeVarTuple(name)
		.. class:: TypeVarTuple(name, default=<unrepresentable>)

		Type variable tuple. A specialized form of :ref:`type variable <typevar>`
		that enables variadic generics.
Expand DownExpand Up		@@ -1872,14 +1884,26 @@ without the dedicated syntax, as documented below.

		The name of the type variable tuple.

		.. attribute:: __default__

		The default value of the type variable tuple, if any. This attribute is ``None``
		if the type variable tuple has no default, and :class:`types.NoneType`
		if the default is set to ``None``.

		.. versionadded:: 3.13

		.. versionadded:: 3.11

		.. versionchanged:: 3.12

		Type variable tuples can now be declared using the
		:ref:`type parameter <type-params>` syntax introduced by :pep:`695`.

		.. class:: ParamSpec(name, *, bound=None, covariant=False, contravariant=False)
		.. versionchanged:: 3.13

		Support for default values was added.

		.. class:: ParamSpec(name, *, bound=None, covariant=False, contravariant=False, default=<unrepresentable>)

		Parameter specification variable. A specialized version of
		:ref:`type variables <typevar>`.
Expand DownExpand Up		@@ -1948,6 +1972,14 @@ without the dedicated syntax, as documented below.

		The name of the parameter specification.

		.. attribute:: __default__

		The default value of the parameter specification, if any. This attribute is ``None``
		if the parameter specification has no default, and :class:`types.NoneType`
		if the default is set to ``None``.

		.. versionadded:: 3.13

		Parameter specification variables created with ``covariant=True`` or
		``contravariant=True`` can be used to declare covariant or contravariant
		generic types. The ``bound`` argument is also accepted, similar to
Expand All		@@ -1961,6 +1993,10 @@ without the dedicated syntax, as documented below.
		Parameter specifications can now be declared using the
		:ref:`type parameter <type-params>` syntax introduced by :pep:`695`.

		.. versionchanged:: 3.13

		Support for default values was added.

		.. note::
		Only parameter specification variables defined in global scope can
		be pickled.
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1620,15 +1620,18 @@ Type parameter lists

		.. versionadded:: 3.12

		.. versionchanged:: 3.13
		Support for default values was added (see :pep:`696`).

		.. index::
		single: type parameters

		.. productionlist:: python-grammar
		type_params: "[" `type_param` ("," `type_param`)* "]"
		type_param: `typevar` \| `typevartuple` \| `paramspec`
		typevar: `identifier` (":" `expression`)?
		typevartuple: "*" `identifier`
		paramspec: "**" `identifier`
		typevar: `identifier` (":" `expression`)? ("=" `expression`)?
		typevartuple: "*" `identifier` ("=" `expression`)?
		paramspec: "**" `identifier` ("=" `expression`)?

		:ref:`Functions <def>` (including :ref:`coroutines <async def>`),
		:ref:`classes <class>` and :ref:`type aliases <type>` may
Expand DownExpand Up		@@ -1694,19 +1697,29 @@ evaluated in a separate :ref:`annotation scope <annotation-scopes>`.
		:data:`typing.TypeVarTuple`\ s and :data:`typing.ParamSpec`\ s cannot have bounds
		or constraints.

		All three flavors of type parameters can also have a default value, which is used
		when the type parameter is not explicitly provided. This is added by appending
		a single equals sign (``=``) followed by an expression. Like the bounds and
		constraints of type variables, the default value is not evaluated when the
		object is created, but only when the type parameter's ``__default__`` attribute
		is accessed. To this end, the default value is evaluated in a separate
		:ref:`annotation scope <annotation-scopes>`.
JelleZijlstra marked this conversation as resolved. OutdatedShow resolvedHide resolved

		The following example indicates the full set of allowed type parameter declarations::

		def overly_generic[
		SimpleTypeVar,
		TypeVarWithDefault = int,
		TypeVarWithBound: int,
		TypeVarWithConstraints: (str, bytes),
		*SimpleTypeVarTuple,
		**SimpleParamSpec,
		*SimpleTypeVarTuple = (int, float),
		**SimpleParamSpec = (str, bytearray),
		](
		a: SimpleTypeVar,
		b: TypeVarWithBound,
		c: Callable[SimpleParamSpec, TypeVarWithConstraints],
		*d: SimpleTypeVarTuple,
		b: TypeVarWithDefault,
		c: TypeVarWithBound,
		d: Callable[SimpleParamSpec, TypeVarWithConstraints],
		*e: SimpleTypeVarTuple,
		): ...

		.. _generic-functions:
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -205,7 +205,7 @@ Annotation scopes are used in the following contexts:
		* Type parameter lists for :ref:`generic classes <generic-classes>`.
		A generic class's base classes and
		keyword arguments are executed within the annotation scope, but its decorators are not.
		* The boundsandconstraintsfor typevariables
		* The bounds, constraints,anddefault valuesfor typeparameters
		(:ref:`lazily evaluated <lazy-evaluation>`).
		* The value of type aliases (:ref:`lazily evaluated <lazy-evaluation>`).

Expand All		@@ -232,13 +232,17 @@ Annotation scopes differ from function scopes in the following ways:
		.. versionadded:: 3.12
		Annotation scopes were introduced in Python 3.12 as part of :pep:`695`.

		.. versionchanged:: 3.13
		Annotation scopes are now also used for type parameter defaults, as
JelleZijlstra marked this conversation as resolved. OutdatedShow resolvedHide resolved
		introduced by :pep:`696`.

		.. _lazy-evaluation:

		Lazy evaluation
		---------------

		The values of type aliases created through the :keyword:`type` statement are
		lazily evaluated. The same applies to the boundsandconstraints of type
		lazily evaluated. The same applies to the bounds, constraints,anddefault values of type
		variables created through the :ref:`type parameter syntax <type-params>`.
		This means that they are not evaluated when the type alias or type variable is
		created. Instead, they are only evaluated when doing so is necessary to resolve
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -89,6 +89,8 @@ Interpreter improvements:

		New typing features:

		* :pep:`696`: Type parameters (:data:`typing.TypeVar`, :data:`typing.ParamSpec`,
		and :data:`typing.TypeVarTuple`) now support defaults.
Comment on lines +92 to +93 Copy link Member AlexWaygoodApr 23, 2024 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. This feels like a very short description of the changes, considering that it involves a change to CPython's grammar 😃 but we can add a more expansive description later; this is non-blocking
		* :pep:`742`: :data:`typing.TypeIs` was added, providing more intuitive
		type narrowing behavior.

Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -644,21 +644,25 @@ type_params[asdl_type_param_seq*]: '[' t=type_param_seq ']' {
		type_param_seq[asdl_type_param_seq]: a[asdl_type_param_seq]=','.type_param+ [','] { a }

		type_param[type_param_ty] (memo):
		\| a=NAME b=[type_param_bound] { _PyAST_TypeVar(a->v.Name.id, b, EXTRA) }
		\| a=NAME b=[type_param_bound]c=[type_param_default]{ _PyAST_TypeVar(a->v.Name.id, b, c, EXTRA) }
		\| '*' a=NAME colon=':' e=expression {
		RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
		? "cannot use constraints with TypeVarTuple"
		: "cannot use bound with TypeVarTuple")
		}
		\| '*' a=NAME { _PyAST_TypeVarTuple(a->v.Name.id, EXTRA) }
		\| '*' a=NAMEb=[type_param_starred_default]{ _PyAST_TypeVarTuple(a->v.Name.id, b, EXTRA) }
		\| '**' a=NAME colon=':' e=expression {
		RAISE_SYNTAX_ERROR_STARTING_FROM(colon, e->kind == Tuple_kind
		? "cannot use constraints with ParamSpec"
		: "cannot use bound with ParamSpec")
		}
		\| '**' a=NAME { _PyAST_ParamSpec(a->v.Name.id, EXTRA) }
		\| '**' a=NAMEb=[type_param_default]{ _PyAST_ParamSpec(a->v.Name.id, b, EXTRA) }

		type_param_bound[expr_ty]: ':' e=expression { e }
		type_param_default[expr_ty]: '=' e=expression {
		CHECK_VERSION(expr_ty, 13, "Type parameter defaults are", e) }
		type_param_starred_default[expr_ty]: '=' e=star_expression {
		CHECK_VERSION(expr_ty, 13, "Type parameter defaults are", e) }

		# EXPRESSIONS
		# -----------
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -28,8 +28,9 @@
		#define INTRINSIC_TYPEVAR_WITH_BOUND 2
		#define INTRINSIC_TYPEVAR_WITH_CONSTRAINTS 3
		#define INTRINSIC_SET_FUNCTION_TYPE_PARAMS 4
		#define INTRINSIC_SET_TYPEPARAM_DEFAULT 5

		#define MAX_INTRINSIC_24
		#define MAX_INTRINSIC_25

		typedef PyObject (intrinsic_func1)(PyThreadState* tstate, PyObject *value);
		typedef PyObject (intrinsic_func2)(PyThreadState* tstate, PyObject value1, PyObject value2);
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -13,6 +13,7 @@ extern PyObject _Py_make_paramspec(PyThreadState , PyObject *);
		extern PyObject _Py_make_typevartuple(PyThreadState , PyObject *);
		extern PyObject _Py_make_typealias(PyThreadState , PyObject *);
		extern PyObject _Py_subscript_generic(PyThreadState , PyObject *);
		extern PyObject _Py_set_typeparam_default(PyThreadState , PyObject , PyObject );
		extern int _Py_initialize_generic(PyInterpreterState *);
		extern void _Py_clear_generic_types(PyInterpreterState *);

Expand Down