python · JelleZijlstra · Jun 17, 2024 · Jun 17, 2024
diff --git a/Doc/library/symtable.rst b/Doc/library/symtable.rst
@@ -31,21 +31,74 @@ Generating Symbol Tables
 Examining Symbol Tables
 -----------------------
 
+.. class:: SymbolTableType
+
+   An enumeration indicating the type of a :class:`SymbolTable` object.
+
+   .. attribute:: MODULE
+      :value: "module"
+
+      Used for the symbol table of a module.
+
+   .. attribute:: FUNCTION
+      :value: "function"
+
+      Used for the symbol table of a function.
+
+   .. attribute:: CLASS
+      :value: "class"
+
+      Used for the symbol table of a class.
+
+   The following members refer to different flavors of
+   :ref:`annotation scopes <annotation-scopes>`.
+
+   .. attribute:: ANNOTATION
+      :value: "annotation"
+
+      Used for annotations if ``from __future__ import annotations`` is active.
+
+   .. attribute:: TYPE_ALIAS
+      :value: "type alias"
+
+      Used for the symbol table of :keyword:`type` constructions.
+
+   .. attribute:: TYPE_PARAMETERS
+      :value: "type parameters"
+
+      Used for the symbol table of :ref:`generic functions <generic-functions>`
+      or :ref:`generic classes <generic-classes>`.
+
+   .. attribute:: TYPE_VARIABLE
+      :value: "type variable"
+
+      Used for the symbol table of the bound, the constraint tuple or the
+      default value of a single type variable in the formal sense, i.e.,
+      a TypeVar, a TypeVarTuple or a ParamSpec object (the latter two do
+      not support a bound or a constraint tuple).
+
+   .. versionadded:: 3.13
+
 .. class:: SymbolTable
 
    A namespace table for a block.  The constructor is not public.
 
    .. method:: get_type()
 
-      Return the type of the symbol table.  Possible values are ``'class'``,
-      ``'module'``, ``'function'``, ``'annotation'``, ``'TypeVar bound'``,
-      ``'type alias'``, and ``'type parameter'``. The latter four refer to
-      different flavors of :ref:`annotation scopes <annotation-scopes>`.
+      Return the type of the symbol table.  Possible values are members
+      of the :class:`SymbolTableType` enumeration.
 
       .. versionchanged:: 3.12
          Added ``'annotation'``,  ``'TypeVar bound'``, ``'type alias'``,
          and ``'type parameter'`` as possible return values.
 
+      .. versionchanged:: 3.13
+         Return values are members of the :class:`SymbolTableType` enumeration.
+
+         The exact values of the returned string may change in the future,
+         and thus, it is recommended to use :class:`SymbolTableType` members
+         instead of hard-coded strings.
+
    .. method:: get_id()
 
       Return the table's identifier.

diff --git a/Include/internal/pycore_symtable.h b/Include/internal/pycore_symtable.h
@@ -15,11 +15,23 @@ typedef enum _block_type {
     // Used for annotations if 'from __future__ import annotations' is active.
     // Annotation blocks cannot bind names and are not evaluated.
     AnnotationBlock,
-    // Used for generics and type aliases. These work mostly like functions
-    // (see PEP 695 for details). The three different blocks function identically;
-    // they are different enum entries only so that error messages can be more
-    // precise.
-    TypeVarBoundBlock, TypeAliasBlock, TypeParamBlock
+
+    // The following blocks are used for generics and type aliases. These work
+    // mostly like functions (see PEP 695 for details). The three different
+    // blocks function identically; they are different enum entries only so
+    // that error messages can be more precise.
+
+    // The block to enter when processing a "type" (PEP 695) construction,
+    // e.g., "type MyGeneric[T] = list[T]".
+    TypeAliasBlock,
+    // The block to enter when processing a "generic" (PEP 695) object,
+    // e.g., "def foo[T](): pass" or "class A[T]: pass".
+    TypeParametersBlock,
+    // The block to enter when processing the bound, the constraint tuple
+    // or the default value of a single "type variable" in the formal sense,
+    // i.e., a TypeVar, a TypeVarTuple or a ParamSpec object (the latter two
+    // do not support a bound or a constraint tuple).
+    TypeVariableBlock,
 } _Py_block_ty;
 
 typedef enum _comprehension_type {
@@ -82,7 +94,16 @@ typedef struct _symtable_entry {
     PyObject *ste_children;  /* list of child blocks */
     PyObject *ste_directives;/* locations of global and nonlocal statements */
     PyObject *ste_mangled_names; /* set of names for which mangling should be applied */
+
     _Py_block_ty ste_type;
+    // Optional string set by symtable.c and used when reporting errors.
+    // The content of that string is a description of the current "context".
+    //
+    // For instance, if we are processing the default value of the type
+    // variable "T" in "def foo[T = int](): pass", `ste_scope_info` is
+    // set to "a TypeVar default".
+    const char *ste_scope_info;
+
     int ste_nested;      /* true if block is nested */
     unsigned ste_free : 1;        /* true if block has free variables */
     unsigned ste_child_free : 1;  /* true if a child block has free vars,

diff --git a/Lib/symtable.py b/Lib/symtable.py
@@ -6,8 +6,9 @@
      LOCAL, GLOBAL_IMPLICIT, GLOBAL_EXPLICIT, CELL)
 
 import weakref
+from enum import StrEnum
 
-__all__ = ["symtable", "SymbolTable", "Class", "Function", "Symbol"]
+__all__ = ["symtable", "SymbolTableType", "SymbolTable", "Class", "Function", "Symbol"]
 
 def symtable(code, filename, compile_type):
     """ Return the toplevel *SymbolTable* for the source code.
@@ -39,6 +40,16 @@ def __call__(self, table, filename):
 _newSymbolTable = SymbolTableFactory()
 
 
+class SymbolTableType(StrEnum):
+    MODULE = "module"
+    FUNCTION = "function"
+    CLASS = "class"
+    ANNOTATION = "annotation"
+    TYPE_ALIAS = "type alias"
+    TYPE_PARAMETERS = "type parameters"
+    TYPE_VARIABLE = "type variable"
+
+
 class SymbolTable:
 
     def __init__(self, raw_table, filename):
@@ -62,23 +73,23 @@ def __repr__(self):
     def get_type(self):
         """Return the type of the symbol table.
 
-        The values returned are 'class', 'module', 'function',
-        'annotation', 'TypeVar bound', 'type alias', and 'type parameter'.
+        The value returned is one of the values in
+        the ``SymbolTableType`` enumeration.
         """
         if self._table.type == _symtable.TYPE_MODULE:
-            return "module"
+            return SymbolTableType.MODULE
         if self._table.type == _symtable.TYPE_FUNCTION:
-            return "function"
+            return SymbolTableType.FUNCTION
         if self._table.type == _symtable.TYPE_CLASS:
-            return "class"
+            return SymbolTableType.CLASS
         if self._table.type == _symtable.TYPE_ANNOTATION:
-            return "annotation"
-        if self._table.type == _symtable.TYPE_TYPE_VAR_BOUND:
-            return "TypeVar bound"
+            return SymbolTableType.ANNOTATION
         if self._table.type == _symtable.TYPE_TYPE_ALIAS:
-            return "type alias"
-        if self._table.type == _symtable.TYPE_TYPE_PARAM:
-            return "type parameter"
+            return SymbolTableType.TYPE_ALIAS
+        if self._table.type == _symtable.TYPE_TYPE_PARAMETERS:
+            return SymbolTableType.TYPE_PARAMETERS
+        if self._table.type == _symtable.TYPE_TYPE_VARIABLE:
+            return SymbolTableType.TYPE_VARIABLE
         assert False, f"unexpected type: {self._table.type}"
 
     def get_id(self):

diff --git a/Lib/test/test_symtable.py b/Lib/test/test_symtable.py
@@ -49,7 +49,7 @@ def namespace_test(): pass
 def generic_spam[T](a):
     pass
 
-class GenericMine[T: int]:
+class GenericMine[T: int, U: (int, str) = int]:
     pass
 """
 
@@ -78,6 +78,7 @@ class SymtableTest(unittest.TestCase):
     GenericMine = find_block(top, "GenericMine")
     GenericMine_inner = find_block(GenericMine, "GenericMine")
     T = find_block(GenericMine, "T")
+    U = find_block(GenericMine, "U")
 
     def test_type(self):
         self.assertEqual(self.top.get_type(), "module")
@@ -87,13 +88,14 @@ def test_type(self):
         self.assertEqual(self.internal.get_type(), "function")
         self.assertEqual(self.foo.get_type(), "function")
         self.assertEqual(self.Alias.get_type(), "type alias")
-        self.assertEqual(self.GenericAlias.get_type(), "type parameter")
+        self.assertEqual(self.GenericAlias.get_type(), "type parameters")
         self.assertEqual(self.GenericAlias_inner.get_type(), "type alias")
-        self.assertEqual(self.generic_spam.get_type(), "type parameter")
+        self.assertEqual(self.generic_spam.get_type(), "type parameters")
         self.assertEqual(self.generic_spam_inner.get_type(), "function")
-        self.assertEqual(self.GenericMine.get_type(), "type parameter")
+        self.assertEqual(self.GenericMine.get_type(), "type parameters")
         self.assertEqual(self.GenericMine_inner.get_type(), "class")
-        self.assertEqual(self.T.get_type(), "TypeVar bound")
+        self.assertEqual(self.T.get_type(), "type variable")
+        self.assertEqual(self.U.get_type(), "type variable")
 
     def test_id(self):
         self.assertGreater(self.top.get_id(), 0)

diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
@@ -2046,16 +2046,91 @@ def f(x: *b)
    ...
    SyntaxError: Type parameter list cannot be empty
 
+   >>> def f[T: (x:=3)](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar bound
+
+   >>> def f[T: ((x:= 3), int)](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar constraint
+
+   >>> def f[T = ((x:=3))](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar default
+
+   >>> async def f[T: (x:=3)](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar bound
+
+   >>> async def f[T: ((x:= 3), int)](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar constraint
+
+   >>> async def f[T = ((x:=3))](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar default
+
    >>> type A[T: (x:=3)] = int
    Traceback (most recent call last):
       ...
    SyntaxError: named expression cannot be used within a TypeVar bound
 
+   >>> type A[T: ((x:= 3), int)] = int
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar constraint
+
+   >>> type A[T = ((x:=3))] = int
+   Traceback (most recent call last):
+      ...
+   SyntaxError: named expression cannot be used within a TypeVar default
+
+   >>> def f[T: (yield)](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar bound
+
+   >>> def f[T: (int, (yield))](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar constraint
+
+   >>> def f[T = (yield)](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar default
+
+   >>> def f[*Ts = (yield)](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVarTuple default
+
+   >>> def f[**P = [(yield), int]](): pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a ParamSpec default
+
    >>> type A[T: (yield 3)] = int
    Traceback (most recent call last):
       ...
    SyntaxError: yield expression cannot be used within a TypeVar bound
 
+   >>> type A[T: (int, (yield 3))] = int
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar constraint
+
+   >>> type A[T = (yield 3)] = int
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar default
+
    >>> type A[T: (await 3)] = int
    Traceback (most recent call last):
       ...
@@ -2066,6 +2141,31 @@ def f(x: *b)
       ...
    SyntaxError: yield expression cannot be used within a TypeVar bound
 
+   >>> class A[T: (yield 3)]: pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar bound
+
+   >>> class A[T: (int, (yield 3))]: pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar constraint
+
+   >>> class A[T = (yield)]: pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVar default
+
+   >>> class A[*Ts = (yield)]: pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a TypeVarTuple default
+
+   >>> class A[**P = [(yield), int]]: pass
+   Traceback (most recent call last):
+      ...
+   SyntaxError: yield expression cannot be used within a ParamSpec default
+
    >>> type A = (x := 3)
    Traceback (most recent call last):
       ...

diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-06-03-13-48-44.gh-issue-119933.Kc0HG5.rst b/Misc/NEWS.d/next/Core and Builtins/2024-06-03-13-48-44.gh-issue-119933.Kc0HG5.rst
@@ -0,0 +1,4 @@
+Improve :exc:`SyntaxError` messages for invalid expressions in a type
+parameters bound, a type parameter constraint tuple or a default type
+parameter.
+Patch by Bénédikt Tran.
diff --git a/Misc/NEWS.d/next/Library/2024-06-05-11-39-21.gh-issue-119933.ooJXQV.rst b/Misc/NEWS.d/next/Library/2024-06-05-11-39-21.gh-issue-119933.ooJXQV.rst
@@ -0,0 +1,3 @@
+Add the :class:`symtable.SymbolTableType` enumeration to represent the
+possible outputs of the :class:`symtable.SymbolTable.get_type` method. Patch
+by Bénédikt Tran.
diff --git a/Modules/symtablemodule.c b/Modules/symtablemodule.c
@@ -88,11 +88,11 @@ symtable_init_constants(PyObject *m)
         return -1;
     if (PyModule_AddIntConstant(m, "TYPE_ANNOTATION", AnnotationBlock) < 0)
         return -1;
-    if (PyModule_AddIntConstant(m, "TYPE_TYPE_VAR_BOUND", TypeVarBoundBlock) < 0)
-        return -1;
     if (PyModule_AddIntConstant(m, "TYPE_TYPE_ALIAS", TypeAliasBlock) < 0)
         return -1;
-    if (PyModule_AddIntConstant(m, "TYPE_TYPE_PARAM", TypeParamBlock) < 0)
+    if (PyModule_AddIntConstant(m, "TYPE_TYPE_PARAMETERS", TypeParametersBlock) < 0)
+        return -1;
+    if (PyModule_AddIntConstant(m, "TYPE_TYPE_VARIABLE", TypeVariableBlock) < 0)
         return -1;
 
     if (PyModule_AddIntMacro(m, LOCAL) < 0) return -1;