Split stdlib into Python 2 and 3 versions (#5442)

All new files in stdlib/@python2 are straight copies of the
corresponding files in stdlib.

stdlib/@python2/bz2.pyi

@@ -0,0 +1,78 @@
+import io
+import sys
+from _typeshed import AnyPath, ReadableBuffer, WriteableBuffer
+from typing import IO, Any, Iterable, List, Optional, TextIO, TypeVar, Union, overload
+from typing_extensions import Literal, SupportsIndex
+
+_PathOrFile = Union[AnyPath, IO[bytes]]
+_T = TypeVar("_T")
+
+def compress(data: bytes, compresslevel: int = ...) -> bytes: ...
+def decompress(data: bytes) -> bytes: ...
+
+if sys.version_info >= (3, 3):
+    _OpenBinaryMode = Literal["r", "rb", "w", "wb", "x", "xb", "a", "ab"]
+    _OpenTextMode = Literal["rt", "wt", "xt", "at"]
+    @overload
+    def open(
+        filename: _PathOrFile,
+        mode: _OpenBinaryMode = ...,
+        compresslevel: int = ...,
+        encoding: None = ...,
+        errors: None = ...,
+        newline: None = ...,
+    ) -> BZ2File: ...
+    @overload
+    def open(
+        filename: AnyPath,
+        mode: _OpenTextMode,
+        compresslevel: int = ...,
+        encoding: Optional[str] = ...,
+        errors: Optional[str] = ...,
+        newline: Optional[str] = ...,
+    ) -> TextIO: ...
+    @overload
+    def open(
+        filename: _PathOrFile,
+        mode: str,
+        compresslevel: int = ...,
+        encoding: Optional[str] = ...,
+        errors: Optional[str] = ...,
+        newline: Optional[str] = ...,
+    ) -> Union[BZ2File, TextIO]: ...
+
+class BZ2File(io.BufferedIOBase, IO[bytes]):
+    def __enter__(self: _T) -> _T: ...
+    if sys.version_info >= (3, 9):
+        def __init__(self, filename: _PathOrFile, mode: str = ..., *, compresslevel: int = ...) -> None: ...
+    else:
+        def __init__(
+            self, filename: _PathOrFile, mode: str = ..., buffering: Optional[Any] = ..., compresslevel: int = ...
+        ) -> None: ...
+    def read(self, size: Optional[int] = ...) -> bytes: ...
+    def read1(self, size: int = ...) -> bytes: ...
+    def readline(self, size: SupportsIndex = ...) -> bytes: ...  # type: ignore
+    def readinto(self, b: WriteableBuffer) -> int: ...
+    def readlines(self, size: SupportsIndex = ...) -> List[bytes]: ...
+    def seek(self, offset: int, whence: int = ...) -> int: ...
+    def write(self, data: ReadableBuffer) -> int: ...
+    def writelines(self, seq: Iterable[ReadableBuffer]) -> None: ...
+
+class BZ2Compressor(object):
+    def __init__(self, compresslevel: int = ...) -> None: ...
+    def compress(self, __data: bytes) -> bytes: ...
+    def flush(self) -> bytes: ...
+
+class BZ2Decompressor(object):
+    if sys.version_info >= (3, 5):
+        def decompress(self, data: bytes, max_length: int = ...) -> bytes: ...
+    else:
+        def decompress(self, data: bytes) -> bytes: ...
+    if sys.version_info >= (3, 3):
+        @property
+        def eof(self) -> bool: ...
+    if sys.version_info >= (3, 5):
+        @property
+        def needs_input(self) -> bool: ...
+    @property
+    def unused_data(self) -> bytes: ...