Update array with more precise type for typecodes (#3994)

Fixes #3946

stdlib/2and3/array.pyi

@@ -5,6 +5,12 @@
 import sys
 from typing import (Any, BinaryIO, Generic, Iterable, Iterator, List, MutableSequence,
                     overload, Text, Tuple, TypeVar, Union)
+from typing_extensions import Literal
+
+_IntTypeCode = Literal['b', 'B', 'h', 'H', 'i', 'I', 'l', 'L', 'q', 'Q']
+_FloatTypeCode = Literal['f', 'd']
+_UnicodeTypeCode = Literal['u']
+_TypeCode = Union[_IntTypeCode, _FloatTypeCode, _UnicodeTypeCode]
 
 _T = TypeVar('_T', int, float, Text)
 
@@ -12,8 +18,18 @@ if sys.version_info >= (3,):
     typecodes: str
 
 class array(MutableSequence[_T], Generic[_T]):
-    typecode: str
+    typecode: _TypeCode
     itemsize: int
+    @overload
+    def __init__(self: array[int], typecode: _IntTypeCode,
+                 __initializer: Union[bytes, Iterable[_T]] = ...) -> None: ...
+    @overload
+    def __init__(self: array[float], typecode: _FloatTypeCode,
+                 __initializer: Union[bytes, Iterable[_T]] = ...) -> None: ...
+    @overload
+    def __init__(self: array[Text], typecode: _UnicodeTypeCode,
+                 __initializer: Union[bytes, Iterable[_T]] = ...) -> None: ...
+    @overload
     def __init__(self, typecode: str,
                  __initializer: Union[bytes, Iterable[_T]] = ...) -> None: ...
     def append(self, __v: _T) -> None: ...