[3.9] bpo-42630: Improve error reporting in Tkinter for absent default root (GH-23781) (GH-23853)

* 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.

(cherry picked from commit 3d569fd6dccf9f582bafaca04d3535094cae393e)

1 files changed, 3 insertions, 3 deletions

diff --git a/Lib/tkinter/font.py b/Lib/tkinter/font.py
index 15ad7ab..2b58030 100644
--- a/Lib/tkinter/font.py
+++ b/Lib/tkinter/font.py
@@ -69,7 +69,7 @@ class Font:
     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
@@ -180,7 +180,7 @@ class Font:
 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)
@@ -190,7 +190,7 @@ 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"))