bpo-42328: Fix tkinter.ttk.Style.map(). (GH-23300)

The function accepts now the representation of the default state as
empty sequence (as returned by Style.map()).
The structure of the result is now the same on all platform
and does not depend on the value of wantobjects.

Lib/tkinter/ttk.py

@@ -81,8 +81,6 @@ def _mapdict_values(items):
     #   ['active selected', 'grey', 'focus', [1, 2, 3, 4]]
     opt_val = []
     for *state, val in items:
-        # hacks for backward compatibility
-        state[0] # raise IndexError if empty
         if len(state) == 1:
             # if it is empty (something that evaluates to False), then
             # format it to Tcl code to denote the "normal" state
@@ -243,19 +241,22 @@ def _script_from_settings(settings):
 def _list_from_statespec(stuple):
     """Construct a list from the given statespec tuple according to the
     accepted statespec accepted by _format_mapdict."""
-    nval = []
-    for val in stuple:
-        typename = getattr(val, 'typename', None)
-        if typename is None:
-            nval.append(val)
-        else: # this is a Tcl object
+    if isinstance(stuple, str):
+        return stuple
+    result = []
+    it = iter(stuple)
+    for state, val in zip(it, it):
+        if hasattr(state, 'typename'):  # this is a Tcl object
+            state = str(state).split()
+        elif isinstance(state, str):
+            state = state.split()
+        elif not isinstance(state, (tuple, list)):
+            state = (state,)
+        if hasattr(val, 'typename'):
             val = str(val)
-            if typename == 'StateSpec':
-                val = val.split()
-            nval.append(val)
+        result.append((*state, val))
 
-    it = iter(nval)
-    return [_flatten(spec) for spec in zip(it, it)]
+    return result
 
 def _list_from_layouttuple(tk, ltuple):
     """Construct a list from the tuple returned by ttk::layout, this is
@@ -395,13 +396,12 @@ class Style(object):
         or something else of your preference. A statespec is compound of
         one or more states and then a value."""
         if query_opt is not None:
-            return _list_from_statespec(self.tk.splitlist(
-                self.tk.call(self._name, "map", style, '-%s' % query_opt)))
+            result = self.tk.call(self._name, "map", style, '-%s' % query_opt)
+            return _list_from_statespec(self.tk.splitlist(result))
 
-        return _splitdict(
-            self.tk,
-            self.tk.call(self._name, "map", style, *_format_mapdict(kw)),
-            conv=_tclobj_to_py)
+        result = self.tk.call(self._name, "map", style, *_format_mapdict(kw))
+        return {k: _list_from_statespec(self.tk.splitlist(v))
+                for k, v in _splitdict(self.tk, result).items()}
 
 
     def lookup(self, style, option, state=None, default=None):