io: minor fixes for arguments (#3642)

stdlib/3/io.pyi

@@ -3,6 +3,7 @@ from typing import (
 )
 import builtins
 import codecs
+import sys
 from mmap import mmap
 from types import TracebackType
 from typing import TypeVar
@@ -102,7 +103,7 @@ class BytesIO(BinaryIO):
     # TODO should be the next line instead
     # def writelines(self, lines: List[Union[bytes, bytearray]]) -> None: ...
     def writelines(self, lines: Any) -> None: ...
-    def readline(self, size: int = ...) -> bytes: ...
+    def readline(self, __size: Optional[int] = ...) -> bytes: ...
     def __del__(self) -> None: ...
     closed: bool
     # copied from BufferedIOBase
@@ -111,7 +112,10 @@ class BytesIO(BinaryIO):
     def write(self, b: Union[bytes, bytearray]) -> int: ...
     def readinto1(self, b: _bytearray_like) -> int: ...
     def read(self, size: Optional[int] = ...) -> bytes: ...
-    def read1(self, size: int = ...) -> bytes: ...
+    if sys.version_info >= (3, 7):
+        def read1(self, __size: Optional[int] = ...) -> bytes: ...
+    else:
+        def read1(self, __size: Optional[int]) -> bytes: ...
 
 class BufferedReader(BufferedIOBase):
     def __init__(self, raw: RawIOBase, buffer_size: int = ...) -> None: ...