bpo-42630: Improve error reporting in Tkinter for absent default root (GH-23781)

* Tkinter functions and constructors which need a default root window
  raise now RuntimeError with descriptive message instead of obscure
  AttributeError or NameError if it is not created yet or cannot
  be created automatically.

* Add tests for all functions which use default root window.

* Fix import in the pynche script.

Author: serhiy-storchaka

Lib/idlelib/pyshell.py

@@ -1061,8 +1061,10 @@ def begin(self):
                    (sys.version, sys.platform, self.COPYRIGHT, nosub))
         self.text.focus_force()
         self.showprompt()
+        # User code should use separate default Tk root window
         import tkinter
-        tkinter._default_root = None # 03Jan04 KBK What's this?
+        tkinter._support_default_root = True
+        tkinter._default_root = None
         return True
 
     def stop_readline(self):

Lib/test/test_idle.py

@@ -20,5 +20,5 @@
 if __name__ == '__main__':
     tk.NoDefaultRoot()
     unittest.main(exit=False)
-    tk._support_default_root = 1
+    tk._support_default_root = True
     tk._default_root = None

Lib/tkinter/__init__.py

@@ -270,7 +270,7 @@ def __repr__(self):
         )
 
 
-_support_default_root = 1
+_support_default_root = True
 _default_root = None
 
 
@@ -280,13 +280,26 @@ def NoDefaultRoot():
     Call this function to inhibit that the first instance of
     Tk is used for windows without an explicit parent window.
     """
-    global _support_default_root
-    _support_default_root = 0
-    global _default_root
+    global _support_default_root, _default_root
+    _support_default_root = False
+    # Delete, so any use of _default_root will immediately raise an exception.
+    # Rebind before deletion, so repeated calls will not fail.
     _default_root = None
     del _default_root
 
 
+def _get_default_root(what=None):
+    if not _support_default_root:
+        raise RuntimeError("No master specified and tkinter is "
+                           "configured to not support default root")
+    if not _default_root:
+        if what:
+            raise RuntimeError(f"Too early to {what}: no default root window")
+        root = Tk()
+        assert _default_root is root
+    return _default_root
+
+
 def _tkerror(err):
     """Internal function."""
     pass
@@ -330,7 +343,7 @@ def __init__(self, master=None, value=None, name=None):
             raise TypeError("name must be a string")
         global _varnum
         if not master:
-            master = _default_root
+            master = _get_default_root('create variable')
         self._root = master._root()
         self._tk = master.tk
         if name:
@@ -591,7 +604,7 @@ def get(self):
 
 def mainloop(n=0):
     """Run the main loop of Tcl."""
-    _default_root.tk.mainloop(n)
+    _get_default_root('run the main loop').tk.mainloop(n)
 
 
 getint = int
@@ -600,9 +613,9 @@ def mainloop(n=0):
 
 
 def getboolean(s):
-    """Convert true and false to integer values 1 and 0."""
+    """Convert Tcl object to True or False."""
     try:
-        return _default_root.tk.getboolean(s)
+        return _get_default_root('use getboolean()').tk.getboolean(s)
     except TclError:
         raise ValueError("invalid literal for getboolean()")
 
@@ -2248,7 +2261,7 @@ def __init__(self, screenName=None, baseName=None, className='Tk',
         is the name of the widget class."""
         self.master = None
         self.children = {}
-        self._tkloaded = 0
+        self._tkloaded = False
         # to avoid recursions in the getattr code in case of failure, we
         # ensure that self.tk is always _something_.
         self.tk = None
@@ -2272,7 +2285,7 @@ def loadtk(self):
             self._loadtk()
 
     def _loadtk(self):
-        self._tkloaded = 1
+        self._tkloaded = True
         global _default_root
         # Version sanity checks
         tk_version = self.tk.getvar('tk_version')
@@ -2521,12 +2534,8 @@ class BaseWidget(Misc):
 
     def _setup(self, master, cnf):
         """Internal function. Sets up information about children."""
-        if _support_default_root:
-            global _default_root
-            if not master:
-                if not _default_root:
-                    _default_root = Tk()
-                master = _default_root
+        if not master:
+            master = _get_default_root()
         self.master = master
         self.tk = master.tk
         name = None
@@ -3990,9 +3999,7 @@ class Image:
     def __init__(self, imgtype, name=None, cnf={}, master=None, **kw):
         self.name = None
         if not master:
-            master = _default_root
-            if not master:
-                raise RuntimeError('Too early to create image')
+            master = _get_default_root('create image')
         self.tk = getattr(master, 'tk', master)
         if not name:
             Image._last_id += 1
@@ -4146,11 +4153,13 @@ def __init__(self, name=None, cnf={}, master=None, **kw):
 
 
 def image_names():
-    return _default_root.tk.splitlist(_default_root.tk.call('image', 'names'))
+    tk = _get_default_root('use image_names()').tk
+    return tk.splitlist(tk.call('image', 'names'))
 
 
 def image_types():
-    return _default_root.tk.splitlist(_default_root.tk.call('image', 'types'))
+    tk = _get_default_root('use image_types()').tk
+    return tk.splitlist(tk.call('image', 'types'))
 
 
 class Spinbox(Widget, XView):

Lib/tkinter/commondialog.py

@@ -18,10 +18,10 @@ class Dialog:
     command = None
 
     def __init__(self, master=None, **options):
+        if not master:
+            master = options.get('parent')
         self.master = master
         self.options = options
-        if not master and options.get('parent'):
-            self.master = options['parent']
 
     def _fixoptions(self):
         pass # hook

Lib/tkinter/font.py

@@ -69,7 +69,7 @@ def _mkdict(self, args):
     def __init__(self, root=None, font=None, name=None, exists=False,
                  **options):
         if not root:
-            root = tkinter._default_root
+            root = tkinter._get_default_root('use font')
         tk = getattr(root, 'tk', root)
         if font:
             # get actual settings corresponding to the given font
@@ -184,7 +184,7 @@ def metrics(self, *options, **kw):
 def families(root=None, displayof=None):
     "Get font families (as a tuple)"
     if not root:
-        root = tkinter._default_root
+        root = tkinter._get_default_root('use font.families()')
     args = ()
     if displayof:
         args = ('-displayof', displayof)
@@ -194,7 +194,7 @@ def families(root=None, displayof=None):
 def names(root=None):
     "Get names of defined fonts (as a tuple)"
     if not root:
-        root = tkinter._default_root
+        root = tkinter._get_default_root('use font.names()')
     return root.tk.splitlist(root.tk.call("font", "names"))
 
 

Lib/tkinter/simpledialog.py

@@ -24,9 +24,7 @@
 """
 
 from tkinter import *
-from tkinter import messagebox
-
-import tkinter # used at _QueryDialog for tkinter._default_root
+from tkinter import messagebox, _get_default_root
 
 
 class SimpleDialog:
@@ -128,13 +126,17 @@ def __init__(self, parent, title = None):
 
             title -- the dialog title
         '''
-        Toplevel.__init__(self, parent)
+        master = parent
+        if not master:
+            master = _get_default_root('create dialog window')
+
+        Toplevel.__init__(self, master)
 
         self.withdraw() # remain invisible for now
-        # If the master is not viewable, don't
+        # If the parent is not viewable, don't
         # make the child transient, or else it
         # would be opened withdrawn
-        if parent.winfo_viewable():
+        if parent is not None and parent.winfo_viewable():
             self.transient(parent)
 
         if title:
@@ -155,7 +157,7 @@ def __init__(self, parent, title = None):
 
         self.protocol("WM_DELETE_WINDOW", self.cancel)
 
-        if self.parent is not None:
+        if parent is not None:
             self.geometry("+%d+%d" % (parent.winfo_rootx()+50,
                                       parent.winfo_rooty()+50))
 
@@ -259,9 +261,6 @@ def __init__(self, title, prompt,
                  minvalue = None, maxvalue = None,
                  parent = None):
 
-        if not parent:
-            parent = tkinter._default_root
-
         self.prompt   = prompt
         self.minvalue = minvalue
         self.maxvalue = maxvalue

Lib/tkinter/test/support.py

@@ -36,6 +36,33 @@ def tearDown(self):
             w.destroy()
         self.root.withdraw()
 
+
+class AbstractDefaultRootTest:
+
+    def setUp(self):
+        self._old_support_default_root = tkinter._support_default_root
+        destroy_default_root()
+        tkinter._support_default_root = True
+        self.wantobjects = tkinter.wantobjects
+
+    def tearDown(self):
+        destroy_default_root()
+        tkinter._default_root = None
+        tkinter._support_default_root = self._old_support_default_root
+
+    def _test_widget(self, constructor):
+        # no master passing
+        x = constructor()
+        self.assertIsNotNone(tkinter._default_root)
+        self.assertIs(x.master, tkinter._default_root)
+        self.assertIs(x.tk, tkinter._default_root.tk)
+        x.destroy()
+        destroy_default_root()
+        tkinter.NoDefaultRoot()
+        self.assertRaises(RuntimeError, constructor)
+        self.assertFalse(hasattr(tkinter, '_default_root'))
+
+
 def destroy_default_root():
     if getattr(tkinter, '_default_root', None):
         tkinter._default_root.update_idletasks()

Lib/tkinter/test/test_tkinter/test_font.py

@@ -2,7 +2,7 @@
 import tkinter
 from tkinter import font
 from test.support import requires, run_unittest, gc_collect, ALWAYS_EQ
-from tkinter.test.support import AbstractTkTest
+from tkinter.test.support import AbstractTkTest, AbstractDefaultRootTest
 
 requires('gui')
 
@@ -107,7 +107,37 @@ def test_repr(self):
         )
 
 
-tests_gui = (FontTest, )
+class DefaultRootTest(AbstractDefaultRootTest, unittest.TestCase):
+
+    def test_families(self):
+        self.assertRaises(RuntimeError, font.families)
+        root = tkinter.Tk()
+        families = font.families()
+        self.assertIsInstance(families, tuple)
+        self.assertTrue(families)
+        for family in families:
+            self.assertIsInstance(family, str)
+            self.assertTrue(family)
+        root.destroy()
+        tkinter.NoDefaultRoot()
+        self.assertRaises(RuntimeError, font.families)
+
+    def test_names(self):
+        self.assertRaises(RuntimeError, font.names)
+        root = tkinter.Tk()
+        names = font.names()
+        self.assertIsInstance(names, tuple)
+        self.assertTrue(names)
+        for name in names:
+            self.assertIsInstance(name, str)
+            self.assertTrue(name)
+        self.assertIn(fontname, names)
+        root.destroy()
+        tkinter.NoDefaultRoot()
+        self.assertRaises(RuntimeError, font.names)
+
+
+tests_gui = (FontTest, DefaultRootTest)
 
 if __name__ == "__main__":
     run_unittest(*tests_gui)

Lib/tkinter/test/test_tkinter/test_images.py

@@ -2,7 +2,7 @@
 import tkinter
 from test import support
 from test.support import os_helper
-from tkinter.test.support import AbstractTkTest, requires_tcl
+from tkinter.test.support import AbstractTkTest, AbstractDefaultRootTest, requires_tcl
 
 support.requires('gui')
 
@@ -20,6 +20,47 @@ def test_image_names(self):
         self.assertIsInstance(image_names, tuple)
 
 
+class DefaultRootTest(AbstractDefaultRootTest, unittest.TestCase):
+
+    def test_image_types(self):
+        self.assertRaises(RuntimeError, tkinter.image_types)
+        root = tkinter.Tk()
+        image_types = tkinter.image_types()
+        self.assertIsInstance(image_types, tuple)
+        self.assertIn('photo', image_types)
+        self.assertIn('bitmap', image_types)
+        root.destroy()
+        tkinter.NoDefaultRoot()
+        self.assertRaises(RuntimeError, tkinter.image_types)
+
+    def test_image_names(self):
+        self.assertRaises(RuntimeError, tkinter.image_names)
+        root = tkinter.Tk()
+        image_names = tkinter.image_names()
+        self.assertIsInstance(image_names, tuple)
+        root.destroy()
+        tkinter.NoDefaultRoot()
+        self.assertRaises(RuntimeError, tkinter.image_names)
+
+    def test_image_create_bitmap(self):
+        self.assertRaises(RuntimeError, tkinter.BitmapImage)
+        root = tkinter.Tk()
+        image = tkinter.BitmapImage()
+        self.assertIn(image.name, tkinter.image_names())
+        root.destroy()
+        tkinter.NoDefaultRoot()
+        self.assertRaises(RuntimeError, tkinter.BitmapImage)
+
+    def test_image_create_photo(self):
+        self.assertRaises(RuntimeError, tkinter.PhotoImage)
+        root = tkinter.Tk()
+        image = tkinter.PhotoImage()
+        self.assertIn(image.name, tkinter.image_names())
+        root.destroy()
+        tkinter.NoDefaultRoot()
+        self.assertRaises(RuntimeError, tkinter.PhotoImage)
+
+
 class BitmapImageTest(AbstractTkTest, unittest.TestCase):
 
     @classmethod
@@ -331,7 +372,7 @@ def test_transparency(self):
         self.assertEqual(image.transparency_get(4, 6), False)
 
 
-tests_gui = (MiscTest, BitmapImageTest, PhotoImageTest,)
+tests_gui = (MiscTest, DefaultRootTest, BitmapImageTest, PhotoImageTest,)
 
 if __name__ == "__main__":
     support.run_unittest(*tests_gui)