Issue #15133: _tkinter.tkapp.getboolean() now supports Tcl_Obj and always

returns bool.  tkinter.BooleanVar now validates input values (accepted bool,
int, str, and Tcl_Obj).  tkinter.BooleanVar.get() now always returns bool.

Lib/tkinter/__init__.py

@@ -391,6 +391,11 @@ class BooleanVar(Variable):
         """
         Variable.__init__(self, master, value, name)
 
+    def set(self, value):
+        """Set the variable to VALUE."""
+        return self._tk.globalsetvar(self._name, self._tk.getboolean(value))
+    initialize = set
+
     def get(self):
         """Return the value of the variable as a bool."""
         try: