Add _pydecimal and _decimal stubs (#4003)

stdlib/2and3/decimal.pyi

@@ -35,7 +35,8 @@ if sys.version_info >= (3,):
     MIN_ETINY: int
 
 class DecimalException(ArithmeticError):
-    def handle(self, context: Context, *args: Any) -> Optional[Decimal]: ...
+    if sys.version_info < (3,):
+        def handle(self, context: Context, *args: Any) -> Optional[Decimal]: ...
 
 class Clamped(DecimalException): ...
 
@@ -64,14 +65,14 @@ class Underflow(Inexact, Rounded, Subnormal): ...
 if sys.version_info >= (3,):
     class FloatOperation(DecimalException, TypeError): ...
 
-def setcontext(context: Context) -> None: ...
+def setcontext(__context: Context) -> None: ...
 def getcontext() -> Context: ...
 def localcontext(ctx: Optional[Context] = ...) -> _ContextManager: ...
 
 class Decimal(object):
     def __new__(cls: Type[_DecimalT], value: _DecimalNew = ..., context: Optional[Context] = ...) -> _DecimalT: ...
     @classmethod
-    def from_float(cls, f: float) -> Decimal: ...
+    def from_float(cls, __f: float) -> Decimal: ...
     if sys.version_info >= (3,):
         def __bool__(self) -> bool: ...
     else:
@@ -83,7 +84,7 @@ class Decimal(object):
     def compare(self, other: _Decimal, context: Optional[Context] = ...) -> Decimal: ...
     def __hash__(self) -> int: ...
     def as_tuple(self) -> DecimalTuple: ...
-    if sys.version_info >= (3,):
+    if sys.version_info >= (3, 6):
         def as_integer_ratio(self) -> Tuple[int, int]: ...
 
     def to_eng_string(self, context: Optional[Context] = ...) -> str: ...

stdlib/3/_decimal.pyi

@@ -0,0 +1,2 @@
+
+from decimal import *

stdlib/3/_pydecimal.pyi

@@ -0,0 +1,4 @@
+
+# This is a slight lie, the implementations aren't exactly identical
+# However, in all likelihood, the differences are inconsequential
+from decimal import *

tests/stubtest_whitelists/py35.txt

@@ -21,7 +21,6 @@ codecs.StreamRecoder.seek
 collections.Reversible
 collections.UserString.maketrans
 ctypes.CDLL.__init__
-decimal.Decimal.as_integer_ratio
 fractions.Fraction.__new__  # private _normalize param was made keyword-only in Python 3.6
 gettext.NullTranslations.npgettext
 gettext.NullTranslations.pgettext

tests/stubtest_whitelists/py38.txt

@@ -66,8 +66,6 @@ copy.PyStringMap
 dataclasses.dataclass
 dataclasses.field
 dataclasses.replace
-decimal.Decimal.from_float
-decimal.setcontext
 email.message.MIMEPart.as_string
 enum.Enum._generate_next_value_
 functools.partialmethod.__get__

tests/stubtest_whitelists/py3_common.txt

@@ -154,7 +154,6 @@ curses.COLS
 curses.LINES
 dbm.error
 dbm.ndbm
-decimal.DecimalException.handle
 difflib.SequenceMatcher.__init__
 distutils.archive_util.make_archive
 distutils.archive_util.make_tarball
@@ -523,6 +522,7 @@ zlib.compressobj
 # ==========
 # Whitelist entries that cannot or should not be fixed
 # ==========
+_pydecimal.*  # See comments in file
 ast.NodeVisitor.visit_\w+  # Methods are discovered dynamically, see #3796
 # Weird special builtins that are typed as functions, but aren't functions
 builtins.copyright