more 3.7 features (#2015)

stdlib/3/sys.pyi

@@ -72,6 +72,8 @@ class _flags:
     bytes_warning = 0
     quiet = 0
     hash_randomization = 0
+    if sys.version_info >= (3, 7):
+        dev_mode: int
 
 float_info = ...  # type: _float_info
 class _float_info:

stdlib/3/tkinter/ttk.pyi

@@ -1,3 +1,4 @@
+import sys
 from typing import Any
 import tkinter
 
@@ -105,6 +106,11 @@ class Separator(Widget):
 class Sizegrip(Widget):
     def __init__(self, master=None, **kw): ...
 
+if sys.version_info >= (3, 7):
+    class Spinbox(Entry):
+        def __init__(self, master: Any = ..., **kw: Any) -> None: ...
+        def set(self, value: Any) -> None: ...
+
 class Treeview(Widget, tkinter.XView, tkinter.YView):
     def __init__(self, master=None, **kw): ...
     def bbox(self, item, column=None): ...

stdlib/3/unittest/mock.pyi

@@ -176,3 +176,6 @@ if sys.version_info >= (3, 3):
     class PropertyMock(Mock):
         def __get__(self, obj: Any, obj_type: Any) -> Any: ...
         def __set__(self, obj: Any, val: Any) -> Any: ...
+
+if sys.version_info >= (3, 7):
+    def seal(mock: Any) -> None: ...