BZ2Compressor and BZ2Decompressor live in the _bz2 module

stdlib/@tests/stubtest_allowlists/py310.txt

@@ -3,7 +3,7 @@ _weakref.ProxyType.__reversed__  # Doesn't really exist
 asyncio.base_events.BaseEventLoop.subprocess_exec # BaseEventLoop adds several parameters and stubtest fails on the difference if we add them
 builtins.float.__setformat__  # Internal method for CPython test suite
 builtins.property.__set_name__  # Doesn't actually exist
-bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
+_?bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
 collections\.UserList\.index  # ignoring pos-or-keyword parameter
 configparser.ParsingError.filename
 contextlib.AbstractAsyncContextManager.__class_getitem__

stdlib/@tests/stubtest_allowlists/py311.txt

@@ -5,7 +5,7 @@ _collections_abc.Iterable.__class_getitem__
 _collections_abc.MappingView.__class_getitem__
 _csv.Reader
 _csv.Writer
-bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
+_?bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
 configparser.ParsingError.filename
 collections\.UserList\.index  # ignoring pos-or-keyword parameter
 enum.Enum.__init__

stdlib/@tests/stubtest_allowlists/py38.txt

@@ -14,7 +14,7 @@ asyncio.transports.WriteTransport.get_write_buffer_limits  # Documented. Exists
 asyncio.WriteTransport.get_write_buffer_limits  # Documented. Exists in subclasses, but not in WriteTransport itself
 builtins.float.__set_format__  # Internal method for CPython test suite
 builtins.input  # Incorrect default value in text signature, fixed in 3.10
-bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
+_?bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
 collections.AsyncGenerator.asend  # async at runtime, deliberately not in the stub, see #7491. Pos-only differences also.
 collections.AsyncGenerator.__anext__  # async at runtime, deliberately not in the stub, see #7491
 collections.AsyncGenerator.aclose  # async at runtime, deliberately not in the stub, see #7491

stdlib/@tests/stubtest_allowlists/py39.txt

@@ -3,7 +3,7 @@ ast.ExtSlice.__new__
 ast.Index.__new__
 builtins.float.__setformat__  # Internal method for CPython test suite
 builtins.input  # Incorrect default value in text signature, fixed in 3.10
-bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
+_?bz2.BZ2Decompressor.__init__  # function does not accept parameters but C signature is set
 collections.AsyncGenerator.asend  # async at runtime, deliberately not in the stub, see #7491. Pos-only differences also.
 collections.AsyncGenerator.__anext__  # async at runtime, deliberately not in the stub, see #7491
 collections.AsyncGenerator.aclose  # async at runtime, deliberately not in the stub, see #7491

stdlib/VERSIONS

@@ -24,6 +24,7 @@ _asyncio: 3.0-
 _bisect: 3.0-
 _blake2: 3.6-
 _bootlocale: 3.4-3.9
+_bz2: 3.3-
 _codecs: 3.0-
 _collections_abc: 3.3-
 _compat_pickle: 3.1-

stdlib/_bz2.pyi

@@ -0,0 +1,18 @@
+from _typeshed import ReadableBuffer
+from typing import final
+
+@final
+class BZ2Compressor:
+    def __init__(self, compresslevel: int = 9) -> None: ...
+    def compress(self, data: ReadableBuffer, /) -> bytes: ...
+    def flush(self) -> bytes: ...
+
+@final
+class BZ2Decompressor:
+    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes: ...
+    @property
+    def eof(self) -> bool: ...
+    @property
+    def needs_input(self) -> bool: ...
+    @property
+    def unused_data(self) -> bytes: ...

stdlib/bz2.pyi

@@ -1,9 +1,10 @@
 import _compression
 import sys
+from _bz2 import BZ2Compressor as BZ2Compressor, BZ2Decompressor as BZ2Decompressor
 from _compression import BaseStream
 from _typeshed import ReadableBuffer, StrOrBytesPath, WriteableBuffer
 from collections.abc import Iterable
-from typing import IO, Any, Literal, Protocol, SupportsIndex, TextIO, final, overload
+from typing import IO, Any, Literal, Protocol, SupportsIndex, TextIO, overload
 from typing_extensions import Self, TypeAlias
 
 __all__ = ["BZ2File", "BZ2Compressor", "BZ2Decompressor", "open", "compress", "decompress"]
@@ -128,19 +129,3 @@ class BZ2File(BaseStream, IO[bytes]):
     def seek(self, offset: int, whence: int = 0) -> int: ...
     def write(self, data: ReadableBuffer) -> int: ...
     def writelines(self, seq: Iterable[ReadableBuffer]) -> None: ...
-
-@final
-class BZ2Compressor:
-    def __init__(self, compresslevel: int = 9) -> None: ...
-    def compress(self, data: ReadableBuffer, /) -> bytes: ...
-    def flush(self) -> bytes: ...
-
-@final
-class BZ2Decompressor:
-    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes: ...
-    @property
-    def eof(self) -> bool: ...
-    @property
-    def needs_input(self) -> bool: ...
-    @property
-    def unused_data(self) -> bytes: ...