PEP 800: Disjoint bases

I just posted https://peps.python.org/pep-0800/, which proposes adding an @solid_base decorator to the type system. "Solid bases" are classes that don't allow inheritance from other solid bases, which includes most builtins.

Usually our policy is not to use draft PEPs in typeshed until they are accepted. I think in this case, it's worth making an exception:

Even if type checkers don't support the decorator, they'll still be able to use the stubs with no regression in functionality. They'll just see an identity decorator on some classes. I tried this just now in Add @typing_extensions.solid_base #14443 and CI shows that mypy and pyright are unaffected by the presence of the decorator on int and str. (There are some other CI failures for unrelated reasons.)
While type checkers could implement the feature before typeshed adds @solid_base decorators, the feature will be a lot more useful if standard library classes are correctly marked with the decorator.

If we're in agreement, I would propose to start adding the decorator in typeshed once there is a typing_extensions release with the new feature. I can then also add stubtest support for checking whether the decorator should be present.

I implemented stubtest support (python/mypy#19678). These are the classes that should be marked as disjoint bases (new name for solid bases) in 3.13:

_ast.AST
_asyncio.Future
_asyncio.Task
_collections_abc.MappingView
_csv.Dialect
_csv.Reader
_csv.Writer
_decimal.Context
_decimal.Decimal
_hashlib.HASH
_interpreters.CrossInterpreterBufferView
_io.BufferedRWPair
_io.BufferedRandom
_io.BufferedReader
_io.BufferedWriter
_io.BytesIO
_io.FileIO
_io.IncrementalNewlineDecoder
_io.StringIO
_io.TextIOWrapper
_io._IOBase
_lsprof.Profiler
_multibytecodec.MultibyteIncrementalDecoder
_multibytecodec.MultibyteIncrementalEncoder
_multibytecodec.MultibyteStreamReader
_multibytecodec.MultibyteStreamWriter
_pickle.Pickler
_pickle.Unpickler
_queue.SimpleQueue
_random.Random
_socket.socket
_sqlite3.Connection
_sqlite3.Cursor
_sqlite3.Row
_ssl._SSLContext
_struct.Struct
_thread._local
_threading_local._localimpl
_threading_local.local
_weakref.ReferenceType
array.array
ast.AST
asyncio.BaseTransport
asyncio.Future
asyncio.Handle
asyncio.Task
asyncio.TimerHandle
asyncio.events.Handle
asyncio.events.TimerHandle
asyncio.futures.Future
asyncio.tasks.Task
asyncio.transports.BaseTransport
asyncio.transports._FlowControlMixin
asyncio.trsock.TransportSocket
builtins.AttributeError
builtins.BaseException
builtins.BaseExceptionGroup
builtins.ImportError
builtins.NameError
builtins.OSError
builtins.StopIteration
builtins.SyntaxError
builtins.SystemExit
builtins.UnicodeDecodeError
builtins.UnicodeEncodeError
builtins.UnicodeTranslateError
builtins.bytearray
builtins.bytes
builtins.classmethod
builtins.complex
builtins.dict
builtins.enumerate
builtins.filter
builtins.float
builtins.frozenset
builtins.int
builtins.list
builtins.map
builtins.object
builtins.property
builtins.reversed
builtins.set
builtins.staticmethod
builtins.str
builtins.super
builtins.tuple
builtins.type
builtins.zip
collections.OrderedDict
collections.defaultdict
collections.deque
dataclasses.Field
dataclasses.InitVar
datetime.date
datetime.datetime
datetime.time
datetime.timedelta
decimal.Context
decimal.Decimal
fractions.Fraction
functools.partial
hmac.HMAC
inspect.BoundArguments
inspect.Parameter
inspect.Signature
io.BufferedRWPair
io.BufferedRandom
io.BufferedReader
io.BufferedWriter
io.BytesIO
io.FileIO
io.IncrementalNewlineDecoder
io.StringIO
io.TextIOWrapper
ipaddress.IPv4Address
ipaddress.IPv6Address
itertools.accumulate
itertools.batched
itertools.chain
itertools.combinations
itertools.combinations_with_replacement
itertools.compress
itertools.count
itertools.cycle
itertools.dropwhile
itertools.filterfalse
itertools.groupby
itertools.islice
itertools.pairwise
itertools.permutations
itertools.product
itertools.repeat
itertools.starmap
itertools.takewhile
itertools.zip_longest
mmap.mmap
multiprocessing.managers.Token
pathlib.PurePath
pickle.Pickler
pickle.Unpickler
pickletools.ArgumentDescriptor
pickletools.OpcodeInfo
pickletools.StackObject
queue.SimpleQueue
socket.socket
sqlite3.Connection
sqlite3.Cursor
sqlite3.Row
sqlite3.dbapi2.Connection
sqlite3.dbapi2.Cursor
sqlite3.dbapi2.Row
statistics.NormalDist
struct.Struct
tarfile.TarInfo
traceback.FrameSummary
tracemalloc.Frame
tracemalloc.Statistic
tracemalloc.StatisticDiff
tracemalloc.Trace
tracemalloc.Traceback
types.GenericAlias
types.ModuleType
types.SimpleNamespace
uuid.UUID
weakref.KeyedRef
weakref.ReferenceType
weakref.WeakMethod
xml.dom.expatbuilder.ElementInfo
xml.dom.expatbuilder.FilterCrutch
xml.dom.expatbuilder.FilterVisibilityController
xml.dom.minidom.Attr
xml.dom.minidom.CharacterData
xml.dom.minidom.Document
xml.dom.minidom.Element
xml.dom.minidom.ElementInfo
xml.dom.minidom.Identified
xml.dom.minidom.NamedNodeMap
xml.dom.minidom.ProcessingInstruction
xml.dom.minidom.ReadOnlySequentialNamedNodeMap
xml.dom.minidom.TypeInfo
xml.dom.xmlbuilder.DOMEntityResolver
xml.dom.xmlbuilder.DOMInputSource
xml.etree.ElementTree.Element
xml.etree.ElementTree.TreeBuilder
xml.etree.ElementTree.XMLParser
xml.etree.cElementTree.Element
xml.etree.cElementTree.TreeBuilder
xml.etree.cElementTree.XMLParser
zipfile.ZipInfo
zoneinfo.ZoneInfo

In earlier versions the list is a little different; before Python 3.12, classes that inherit directly from classes implemented in C are generally disjoint bases. This most commonly affects namedtuples.

@disjoint_base has now been added to the stubs (e.g. in #14599, #14683, #14716). Anything else needed here?

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PEP 800: Disjoint bases #14444

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PEP 800: Disjoint bases #14444

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JelleZijlstra commented on Aug 18, 2025

brianschubert commented on Mar 25, 2026

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