bpo-40511: Stop unwanted flashing of IDLE calltips (GH-20910)

They were occurring with both repeated 'force-calltip' invocations and by typing parentheses
 in expressions, strings, and comments in the argument code.

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
(cherry picked from commit da7bb7b4d7)

Co-authored-by: Tal Einat <taleinat+github@gmail.com>

Lib/idlelib/calltip.py

@@ -55,18 +55,50 @@ class Calltip:
             self.open_calltip(False)
 
     def open_calltip(self, evalfuncs):
-        self.remove_calltip_window()
+        """Maybe close an existing calltip and maybe open a new calltip.
 
+        Called from (force_open|try_open|refresh)_calltip_event functions.
+        """
         hp = HyperParser(self.editwin, "insert")
         sur_paren = hp.get_surrounding_brackets('(')
+
+        # If not inside parentheses, no calltip.
         if not sur_paren:
+            self.remove_calltip_window()
             return
+
+        # If a calltip is shown for the current parentheses, do
+        # nothing.
+        if self.active_calltip:
+            opener_line, opener_col = map(int, sur_paren[0].split('.'))
+            if (
+                (opener_line, opener_col) ==
+                (self.active_calltip.parenline, self.active_calltip.parencol)
+            ):
+                return
+
         hp.set_index(sur_paren[0])
-        expression  = hp.get_expression()
+        try:
+            expression = hp.get_expression()
+        except ValueError:
+            expression = None
         if not expression:
+            # No expression before the opening parenthesis, e.g.
+            # because it's in a string or the opener for a tuple:
+            # Do nothing.
             return
+
+        # At this point, the current index is after an opening
+        # parenthesis, in a section of code, preceded by a valid
+        # expression. If there is a calltip shown, it's not for the
+        # same index and should be closed.
+        self.remove_calltip_window()
+
+        # Simple, fast heuristic: If the preceding expression includes
+        # an opening parenthesis, it likely includes a function call.
         if not evalfuncs and (expression.find('(') != -1):
             return
+
         argspec = self.fetch_tip(expression)
         if not argspec:
             return