bpo-33610: Edit idlelib.codecontext (GH-23773)

Add sentence to module docstring and import tkinter items.
(cherry picked from commit 6f79e60)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Lib/idlelib/codecontext.py

@@ -7,11 +7,14 @@
 enclosing block.  The number of hint lines is determined by the maxlines
 variable in the codecontext section of config-extensions.def. Lines which do
 not open blocks are not shown in the context hints pane.
+
+For EditorWindows, <<toggle-code-context>> is bound to CodeContext(self).
+toggle_code_context_event.
 """
 import re
 from sys import maxsize as INFINITY
 
-import tkinter
+from tkinter import Frame, Text, TclError
 from tkinter.constants import NSEW, SUNKEN
 
 from idlelib.config import idleConf
@@ -83,7 +86,7 @@ def __del__(self):
         if self.t1 is not None:
             try:
                 self.text.after_cancel(self.t1)
-            except tkinter.TclError:  # pragma: no cover
+            except TclError:  # pragma: no cover
                 pass
             self.t1 = None
 
@@ -111,7 +114,7 @@ def toggle_code_context_event(self, event=None):
                 padx += widget.tk.getint(info['padx'])
                 padx += widget.tk.getint(widget.cget('padx'))
                 border += widget.tk.getint(widget.cget('border'))
-            context = self.context = tkinter.Text(
+            context = self.context = Text(
                 self.editwin.text_frame,
                 height=1,
                 width=1,  # Don't request more than we get.
@@ -127,7 +130,7 @@ def toggle_code_context_event(self, event=None):
 
             line_number_colors = idleConf.GetHighlight(idleConf.CurrentTheme(),
                                                        'linenumber')
-            self.cell00 = tkinter.Frame(self.editwin.text_frame,
+            self.cell00 = Frame(self.editwin.text_frame,
                                         bg=line_number_colors['background'])
             self.cell00.grid(row=0, column=0, sticky=NSEW)
             menu_status = 'Hide'
@@ -221,7 +224,7 @@ def jumptoline(self, event=None):
         """
         try:
             self.context.index("sel.first")
-        except tkinter.TclError:
+        except TclError:
             lines = len(self.info)
             if lines == 1:  # No context lines are showing.
                 newtop = 1