python · encukou · Feb 24, 2026 · Feb 24, 2026
@@ -29,79 +29,39 @@ def __get__(self, obj, cls):
         return self.getter(None, cls)
 
 
-class UnboundItem:
-    """Represents a cross-interpreter item no longer bound to an interpreter.
+class UnboundBehavior:
+    __slots__ = ('name', '_unboundop')
 
-    An item is unbound when the interpreter that added it to the
-    cross-interpreter container is destroyed.
-    """
-
-    __slots__ = ()
-
-    @classonly
-    def singleton(cls, kind, module, name='UNBOUND'):
-        doc = cls.__doc__
-        if doc:
-            doc = doc.replace(
-                'cross-interpreter container', kind,
-            ).replace(
-                'cross-interpreter', kind,
-            )
-        subclass = type(
-            f'Unbound{kind.capitalize()}Item',
-            (cls,),
-            {
-                "_MODULE": module,
-                "_NAME": name,
-                "__doc__": doc,
-            },
-        )
-        return object.__new__(subclass)
-
-    _MODULE = __name__
-    _NAME = 'UNBOUND'
-
-    def __new__(cls):
-        raise Exception(f'use {cls._MODULE}.{cls._NAME}')
+    def __init__(self, name, *, _unboundop):
+        self.name = name
+        self._unboundop = _unboundop
 
     def __repr__(self):
-        return f'{self._MODULE}.{self._NAME}'
-#        return f'interpreters._queues.UNBOUND'
+        return f'<{self.name}>'
 
 
-UNBOUND = object.__new__(UnboundItem)
-UNBOUND_ERROR = object()
-UNBOUND_REMOVE = object()
+UNBOUND = UnboundBehavior('UNBOUND', _unboundop=3)
+UNBOUND_ERROR = UnboundBehavior('UNBOUND_ERROR', _unboundop=2)
+UNBOUND_REMOVE = UnboundBehavior('UNBOUND_REMOVE', _unboundop=1)
 
-_UNBOUND_CONSTANT_TO_FLAG = {
-    UNBOUND_REMOVE: 1,
-    UNBOUND_ERROR: 2,
-    UNBOUND: 3,
-}
-_UNBOUND_FLAG_TO_CONSTANT = {v: k
-                             for k, v in _UNBOUND_CONSTANT_TO_FLAG.items()}
 
-
-def serialize_unbound(unbound):
-    op = unbound
+def unbound_to_flag(unbounditems):
+    if unbounditems is None:
+        return -1
     try:
-        flag = _UNBOUND_CONSTANT_TO_FLAG[op]
-    except KeyError:
-        raise NotImplementedError(f'unsupported unbound replacement op {op!r}')
-    return flag,
-
+        return unbounditems._unboundop
+    except AttributeError:
+        raise NotImplementedError(
+            f'unsupported unbound replacement object {unbounditems!r}')
 
 def resolve_unbound(flag, exctype_destroyed):
-    try:
-        op = _UNBOUND_FLAG_TO_CONSTANT[flag]
-    except KeyError:
-        raise NotImplementedError(f'unsupported unbound replacement op {flag!r}')
-    if op is UNBOUND_REMOVE:
+    if flag == UNBOUND_REMOVE._unboundop:
         # "remove" not possible here
         raise NotImplementedError
-    elif op is UNBOUND_ERROR:
+    elif flag == UNBOUND_ERROR._unboundop:
         raise exctype_destroyed("item's original interpreter destroyed")
-    elif op is UNBOUND:
+    elif flag == UNBOUND._unboundop:
         return UNBOUND
     else:
-        raise NotImplementedError(repr(op))
+        raise NotImplementedError(
+            f'unsupported unbound replacement op {flag!r}')
@@ -11,7 +11,7 @@
     QueueError, QueueNotFoundError,
 )
 from ._crossinterp import (
-    UNBOUND_ERROR, UNBOUND_REMOVE,
+    UNBOUND, UNBOUND_ERROR, UNBOUND_REMOVE,
 )
 
 __all__ = [
@@ -42,24 +42,12 @@ class ItemInterpreterDestroyed(QueueError,
     """Raised from get() and get_nowait()."""
 
 
-_SHARED_ONLY = 0
-_PICKLED = 1
-
-
-UNBOUND = _crossinterp.UnboundItem.singleton('queue', __name__)
-
-
-def _serialize_unbound(unbound):
-    if unbound is UNBOUND:
-        unbound = _crossinterp.UNBOUND
-    return _crossinterp.serialize_unbound(unbound)
+def _resolve_unbound(flag):
+    return _crossinterp.resolve_unbound(flag, ItemInterpreterDestroyed)
 
 
-def _resolve_unbound(flag):
-    resolved = _crossinterp.resolve_unbound(flag, ItemInterpreterDestroyed)
-    if resolved is _crossinterp.UNBOUND:
-        resolved = UNBOUND
-    return resolved
+_SHARED_ONLY = 0
+_PICKLED = 1
 
 
 def create(maxsize=0, *, unbounditems=UNBOUND):
@@ -71,8 +59,7 @@ def create(maxsize=0, *, unbounditems=UNBOUND):
     supported values.  The default value is UNBOUND, which replaces
     the unbound item.
     """
-    unbound = _serialize_unbound(unbounditems)
-    unboundop, = unbound
+    unboundop = _crossinterp.unbound_to_flag(unbounditems)
     qid = _queues.create(maxsize, unboundop, -1)
     self = Queue(qid)
     self._set_unbound(unboundop, unbounditems)
@@ -211,10 +198,7 @@ def put(self, obj, block=True, timeout=None, *,
         """
         if not block:
             return self.put_nowait(obj, unbounditems=unbounditems)
-        if unbounditems is None:
-            unboundop = -1
-        else:
-            unboundop, = _serialize_unbound(unbounditems)
+        unboundop = _crossinterp.unbound_to_flag(unbounditems)
         if timeout is not None:
             timeout = int(timeout)
             if timeout < 0:
@@ -231,10 +215,7 @@ def put(self, obj, block=True, timeout=None, *,
                 break
 
     def put_nowait(self, obj, *, unbounditems=None):
-        if unbounditems is None:
-            unboundop = -1
-        else:
-            unboundop, = _serialize_unbound(unbounditems)
+        unboundop = _crossinterp.unbound_to_flag(unbounditems)
         _queues.put(self._id, obj, unboundop)
 
     def get(self, block=True, timeout=None, *,

@@ -10,7 +10,7 @@
     ChannelEmptyError, ChannelNotEmptyError,  # noqa: F401
 )
 from concurrent.interpreters._crossinterp import (
-    UNBOUND_ERROR, UNBOUND_REMOVE,
+    UNBOUND, UNBOUND_ERROR, UNBOUND_REMOVE,
 )
 
 
@@ -28,20 +28,8 @@ class ItemInterpreterDestroyed(ChannelError,
     """Raised from get() and get_nowait()."""
 
 
-UNBOUND = _crossinterp.UnboundItem.singleton('queue', __name__)
-
-
-def _serialize_unbound(unbound):
-    if unbound is UNBOUND:
-        unbound = _crossinterp.UNBOUND
-    return _crossinterp.serialize_unbound(unbound)
-
-
 def _resolve_unbound(flag):
-    resolved = _crossinterp.resolve_unbound(flag, ItemInterpreterDestroyed)
-    if resolved is _crossinterp.UNBOUND:
-        resolved = UNBOUND
-    return resolved
+    return _crossinterp.resolve_unbound(flag, ItemInterpreterDestroyed)
 
 
 def create(*, unbounditems=UNBOUND):
@@ -53,8 +41,9 @@ def create(*, unbounditems=UNBOUND):
     See SendChannel.send() for supported values.  The default value
     is UNBOUND, which replaces the unbound item when received.
     """
-    unbound = _serialize_unbound(unbounditems)
-    unboundop, = unbound
+    if unbounditems is None:
+        raise TypeError(f'unbounditems must not be None')
+    unboundop = _crossinterp.unbound_to_flag(unbounditems)
     cid = _channels.create(unboundop, -1)
     recv, send = RecvChannel(cid), SendChannel(cid)
     send._set_unbound(unboundop, unbounditems)
@@ -179,17 +168,6 @@ class SendChannel(_ChannelEnd):
 
     _end = 'send'
 
-#    def __new__(cls, cid, *, _unbound=None):
-#        if _unbound is None:
-#            try:
-#                op = _channels.get_channel_defaults(cid)
-#                _unbound = (op,)
-#            except ChannelNotFoundError:
-#                _unbound = _serialize_unbound(UNBOUND)
-#        self = super().__new__(cls, cid)
-#        self._unbound = _unbound
-#        return self
-
     def _set_unbound(self, op, items=None):
         assert not hasattr(self, '_unbound')
         if items is None:
@@ -219,10 +197,7 @@ def send(self, obj, timeout=None, *,
 
         This blocks until the object is received.
         """
-        if unbounditems is None:
-            unboundop = -1
-        else:
-            unboundop, = _serialize_unbound(unbounditems)
+        unboundop = _crossinterp.unbound_to_flag(unbounditems)
         _channels.send(self._id, obj, unboundop, timeout=timeout, blocking=True)
 
     def send_nowait(self, obj, *,
@@ -233,10 +208,7 @@ def send_nowait(self, obj, *,
         If the object is immediately received then return True
         (else False).  Otherwise this is the same as send().
         """
-        if unbounditems is None:
-            unboundop = -1
-        else:
-            unboundop, = _serialize_unbound(unbounditems)
+        unboundop = _crossinterp.unbound_to_flag(unbounditems)
         # XXX Note that at the moment channel_send() only ever returns
         # None.  This should be fixed when channel_send_wait() is added.
         # See bpo-32604 and gh-19829.
@@ -249,10 +221,7 @@ def send_buffer(self, obj, timeout=None, *,
 
         This blocks until the object is received.
         """
-        if unbounditems is None:
-            unboundop = -1
-        else:
-            unboundop, = _serialize_unbound(unbounditems)
+        unboundop = _crossinterp.unbound_to_flag(unbounditems)
         _channels.send_buffer(self._id, obj, unboundop,
                               timeout=timeout, blocking=True)
 
@@ -264,10 +233,7 @@ def send_buffer_nowait(self, obj, *,
         If the object is immediately received then return True
         (else False).  Otherwise this is the same as send().
         """
-        if unbounditems is None:
-            unboundop = -1
-        else:
-            unboundop, = _serialize_unbound(unbounditems)
+        unboundop = _crossinterp.unbound_to_flag(unbounditems)
         return _channels.send_buffer(self._id, obj, unboundop, blocking=False)
 
     def close(self):

@@ -17,7 +17,7 @@
 )
 
 
-REPLACE = _crossinterp._UNBOUND_CONSTANT_TO_FLAG[_crossinterp.UNBOUND]
+REPLACE = _crossinterp.UNBOUND._unboundop
 
 
 # Additional tests are found in Lib/test/test_interpreters/test_channels.py.

@@ -12,7 +12,7 @@
 from .utils import _run_output, TestBase as _TestBase
 
 HUGE_TIMEOUT = 3600
-REPLACE = _crossinterp._UNBOUND_CONSTANT_TO_FLAG[_crossinterp.UNBOUND]
+REPLACE = _crossinterp.UNBOUND._unboundop
 
 
 def get_num_queues():

diff --git a/Misc/NEWS.d/next/Library/2026-02-24-17-00-13.gh-issue-142414.YnybWr.rst b/Misc/NEWS.d/next/Library/2026-02-24-17-00-13.gh-issue-142414.YnybWr.rst
@@ -0,0 +1,2 @@
+Fix spurious :exc:`KeyError` when :mod:`!concurrent.interpreters._queues` is
+reloaded after import.
-Original file line number
+Diff line change
@@ Expand Up / @@ -17,7 +17,7 @@ @@
     )
-    REPLACE = _crossinterp._UNBOUND_CONSTANT_TO_FLAG[_crossinterp.UNBOUND]
+    REPLACE = _crossinterp.UNBOUND._unboundop
     # Additional tests are found in Lib/test/test_interpreters/test_channels.py.
@@ Expand Down @@
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fix spurious :exc:`KeyError` when :mod:`!concurrent.interpreters._queues` is
		reloaded after import.