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/difflib.pyi

@@ -0,0 +1,153 @@
+import sys
+from typing import (
+    Any,
+    AnyStr,
+    Callable,
+    Generic,
+    Iterable,
+    Iterator,
+    List,
+    NamedTuple,
+    Optional,
+    Sequence,
+    Text,
+    Tuple,
+    TypeVar,
+    Union,
+    overload,
+)
+
+if sys.version_info >= (3, 9):
+    from types import GenericAlias
+
+_T = TypeVar("_T")
+
+if sys.version_info >= (3,):
+    _StrType = Text
+else:
+    # Aliases can't point to type vars, so we need to redeclare AnyStr
+    _StrType = TypeVar("_StrType", Text, bytes)
+
+_JunkCallback = Union[Callable[[Text], bool], Callable[[str], bool]]
+
+class Match(NamedTuple):
+    a: int
+    b: int
+    size: int
+
+class SequenceMatcher(Generic[_T]):
+    def __init__(
+        self, isjunk: Optional[Callable[[_T], bool]] = ..., a: Sequence[_T] = ..., b: Sequence[_T] = ..., autojunk: bool = ...
+    ) -> None: ...
+    def set_seqs(self, a: Sequence[_T], b: Sequence[_T]) -> None: ...
+    def set_seq1(self, a: Sequence[_T]) -> None: ...
+    def set_seq2(self, b: Sequence[_T]) -> None: ...
+    if sys.version_info >= (3, 9):
+        def find_longest_match(
+            self, alo: int = ..., ahi: Optional[int] = ..., blo: int = ..., bhi: Optional[int] = ...
+        ) -> Match: ...
+    else:
+        def find_longest_match(self, alo: int, ahi: int, blo: int, bhi: int) -> Match: ...
+    def get_matching_blocks(self) -> List[Match]: ...
+    def get_opcodes(self) -> List[Tuple[str, int, int, int, int]]: ...
+    def get_grouped_opcodes(self, n: int = ...) -> Iterable[List[Tuple[str, int, int, int, int]]]: ...
+    def ratio(self) -> float: ...
+    def quick_ratio(self) -> float: ...
+    def real_quick_ratio(self) -> float: ...
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, item: Any) -> GenericAlias: ...
+
+# mypy thinks the signatures of the overloads overlap, but the types still work fine
+@overload
+def get_close_matches(  # type: ignore
+    word: AnyStr, possibilities: Iterable[AnyStr], n: int = ..., cutoff: float = ...
+) -> List[AnyStr]: ...
+@overload
+def get_close_matches(
+    word: Sequence[_T], possibilities: Iterable[Sequence[_T]], n: int = ..., cutoff: float = ...
+) -> List[Sequence[_T]]: ...
+
+class Differ:
+    def __init__(self, linejunk: Optional[_JunkCallback] = ..., charjunk: Optional[_JunkCallback] = ...) -> None: ...
+    def compare(self, a: Sequence[_StrType], b: Sequence[_StrType]) -> Iterator[_StrType]: ...
+
+def IS_LINE_JUNK(line: _StrType, pat: Any = ...) -> bool: ...  # pat is undocumented
+def IS_CHARACTER_JUNK(ch: _StrType, ws: _StrType = ...) -> bool: ...  # ws is undocumented
+def unified_diff(
+    a: Sequence[_StrType],
+    b: Sequence[_StrType],
+    fromfile: _StrType = ...,
+    tofile: _StrType = ...,
+    fromfiledate: _StrType = ...,
+    tofiledate: _StrType = ...,
+    n: int = ...,
+    lineterm: _StrType = ...,
+) -> Iterator[_StrType]: ...
+def context_diff(
+    a: Sequence[_StrType],
+    b: Sequence[_StrType],
+    fromfile: _StrType = ...,
+    tofile: _StrType = ...,
+    fromfiledate: _StrType = ...,
+    tofiledate: _StrType = ...,
+    n: int = ...,
+    lineterm: _StrType = ...,
+) -> Iterator[_StrType]: ...
+def ndiff(
+    a: Sequence[_StrType], b: Sequence[_StrType], linejunk: Optional[_JunkCallback] = ..., charjunk: Optional[_JunkCallback] = ...
+) -> Iterator[_StrType]: ...
+
+class HtmlDiff(object):
+    def __init__(
+        self,
+        tabsize: int = ...,
+        wrapcolumn: Optional[int] = ...,
+        linejunk: Optional[_JunkCallback] = ...,
+        charjunk: Optional[_JunkCallback] = ...,
+    ) -> None: ...
+    if sys.version_info >= (3, 5):
+        def make_file(
+            self,
+            fromlines: Sequence[_StrType],
+            tolines: Sequence[_StrType],
+            fromdesc: _StrType = ...,
+            todesc: _StrType = ...,
+            context: bool = ...,
+            numlines: int = ...,
+            *,
+            charset: str = ...,
+        ) -> _StrType: ...
+    else:
+        def make_file(
+            self,
+            fromlines: Sequence[_StrType],
+            tolines: Sequence[_StrType],
+            fromdesc: _StrType = ...,
+            todesc: _StrType = ...,
+            context: bool = ...,
+            numlines: int = ...,
+        ) -> _StrType: ...
+    def make_table(
+        self,
+        fromlines: Sequence[_StrType],
+        tolines: Sequence[_StrType],
+        fromdesc: _StrType = ...,
+        todesc: _StrType = ...,
+        context: bool = ...,
+        numlines: int = ...,
+    ) -> _StrType: ...
+
+def restore(delta: Iterable[_StrType], which: int) -> Iterator[_StrType]: ...
+
+if sys.version_info >= (3, 5):
+    def diff_bytes(
+        dfunc: Callable[[Sequence[str], Sequence[str], str, str, str, str, int, str], Iterator[str]],
+        a: Sequence[bytes],
+        b: Sequence[bytes],
+        fromfile: bytes = ...,
+        tofile: bytes = ...,
+        fromfiledate: bytes = ...,
+        tofiledate: bytes = ...,
+        n: int = ...,
+        lineterm: bytes = ...,
+    ) -> Iterator[bytes]: ...