bpo-33065: Fix problem debugging user classes with __repr__ method (GH-24183)

If __repr__ uses instance attributes, as normal, and one steps
through the __init__ method, debugger may try to get repr before
the instance attributes exist.  reprlib.repr handles the error.
(cherry picked from commit 81f87bbf9f)

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

Lib/idlelib/NEWS.txt

@@ -3,6 +3,8 @@ Released on 2020-12-07?
 ======================================
 
 
+bpo-33065: Fix problem debugging user classes with __repr__ method.
+
 bpo-32631: Finish zzdummy example extension module: make menu entries
 work; add docstrings and tests with 100% coverage.
 

Lib/idlelib/debugger_r.py

@@ -19,7 +19,7 @@
 barrier, in particular frame and traceback objects.
 
 """
-
+import reprlib
 import types
 from idlelib import debugger
 
@@ -170,7 +170,7 @@ def dict_keys_list(self, did):
     def dict_item(self, did, key):
         dict = dicttable[did]
         value = dict[key]
-        value = repr(value) ### can't pickle module 'builtins'
+        value = reprlib.repr(value) ### can't pickle module 'builtins'
         return value
 
 #----------end class IdbAdapter----------
@@ -390,4 +390,4 @@ def restart_subprocess_debugger(rpcclt):
 
 if __name__ == "__main__":
     from unittest import main
-    main('idlelib.idle_test.test_debugger', verbosity=2, exit=False)
+    main('idlelib.idle_test.test_debugger_r', verbosity=2, exit=False)

Lib/idlelib/idle_test/test_debugger_r.py

@@ -25,5 +25,19 @@ def test_init(self):
 # Classes GUIProxy, IdbAdapter, FrameProxy, CodeProxy, DictProxy,
 # GUIAdapter, IdbProxy plus 7 module functions.
 
+class IdbAdapterTest(unittest.TestCase):
+
+    def test_dict_item_noattr(self):  # Issue 33065.
+
+        class BinData:
+            def __repr__(self):
+                return self.length
+
+        debugger_r.dicttable[0] = {'BinData': BinData()}
+        idb = debugger_r.IdbAdapter(None)
+        self.assertTrue(idb.dict_item(0, 'BinData'))
+        debugger_r.dicttable.clear()
+
+
 if __name__ == '__main__':
     unittest.main(verbosity=2)

Misc/NEWS.d/next/IDLE/2021-01-10-01-25-43.bpo-33065.zmyHYJ.rst

@@ -0,0 +1 @@
+Fix problem debugging user classes with __repr__ method.