[3.12] [3.13] gh-123370: Fix the canvas not clearing after running turtledemo.clock (gh-123457) (GH-125653) (#125656)

Rewriting the day and date every tick somehow prevented them from being removed either by clicking STOP or loading another example.  The solution is to rewrite them only when they change.
(cherry picked from commit c124577ebe)

(cherry picked from commit 30d7e9e721)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
Co-authored-by: Wulian <xiguawulian@gmail.com>

Lib/turtledemo/clock.py

@@ -1,8 +1,7 @@
 #!/usr/bin/env python3
-# -*- coding: cp1252 -*-
 """       turtle-example-suite:
 
-             tdemo_clock.py
+           turtledemo/clock.py
 
 Enhanced clock-program, showing date
 and time
@@ -13,6 +12,9 @@ and time
 from turtle import *
 from datetime import datetime
 
+dtfont = "TkFixedFont", 14, "bold"
+current_day = None
+
 def jump(distanz, winkel=0):
     penup()
     right(winkel)
@@ -53,11 +55,23 @@ def clockface(radius):
             jump(-radius)
         rt(6)
 
+def display_date_time():
+    global current_day
+    writer.clear()
+    now = datetime.now()
+    current_day = now.day
+    writer.home()
+    writer.forward(distance=65)
+    writer.write(wochentag(now), align="center", font=dtfont)
+    writer.back(distance=150)
+    writer.write(datum(now), align="center", font=dtfont)
+    writer.forward(distance=85)
+
 def setup():
     global second_hand, minute_hand, hour_hand, writer
     mode("logo")
     make_hand_shape("second_hand", 125, 25)
-    make_hand_shape("minute_hand",  130, 25)
+    make_hand_shape("minute_hand",  115, 25)
     make_hand_shape("hour_hand", 90, 25)
     clockface(160)
     second_hand = Turtle()
@@ -75,10 +89,10 @@ def setup():
         hand.speed(0)
     ht()
     writer = Turtle()
-    #writer.mode("logo")
     writer.ht()
     writer.pu()
     writer.bk(85)
+    display_date_time()
 
 def wochentag(t):
     wochentag = ["Monday", "Tuesday", "Wednesday",
@@ -100,18 +114,11 @@ def tick():
     stunde = t.hour + minute/60.0
     try:
         tracer(False)  # Terminator can occur here
-        writer.clear()
-        writer.home()
-        writer.forward(65)
-        writer.write(wochentag(t),
-                     align="center", font=("Courier", 14, "bold"))
-        writer.back(150)
-        writer.write(datum(t),
-                     align="center", font=("Courier", 14, "bold"))
-        writer.forward(85)
         second_hand.setheading(6*sekunde)  # or here
         minute_hand.setheading(6*minute)
         hour_hand.setheading(30*stunde)
+        if t.day != current_day:
+            display_date_time()
         tracer(True)
         ontimer(tick, 100)
     except Terminator:

Misc/NEWS.d/next/Library/2024-08-28-19-27-35.gh-issue-123370.SPZ9Ux.rst

@@ -0,0 +1 @@
+Fix the canvas not clearing after running turtledemo clock.