By default when getting the search menu, the currently highligted

text is the search term.

Lib/idlelib/SearchDialog.py

@@ -11,7 +11,8 @@ def _setup(text):
     return engine._searchdialog
 
 def find(text):
-    return _setup(text).open(text)
+    pat = text.get("sel.first", "sel.last")
+    return _setup(text).open(text,pat)
 
 def find_again(text):
     return _setup(text).find_again(text)

Lib/idlelib/SearchDialogBase.py

@@ -11,13 +11,16 @@ class SearchDialogBase:
         self.engine = engine
         self.top = None
 
-    def open(self, text):
+    def open(self, text, searchphrase=None):
         self.text = text
         if not self.top:
             self.create_widgets()
         else:
             self.top.deiconify()
             self.top.tkraise()
+        if searchphrase:
+            self.ent.delete(0,"end")
+            self.ent.insert("end",searchphrase)
         self.ent.focus_set()
         self.ent.selection_range(0, "end")
         self.ent.icursor(0)