[3.11] GH-65052: Prevent pdb from crashing when trying to display objects (GH-111002)

(cherry picked from commit c523ce0f43)

Lib/pdb.py

@@ -405,8 +405,9 @@ def preloop(self):
                 # fields are changed to be displayed
                 if newvalue is not oldvalue and newvalue != oldvalue:
                     displaying[expr] = newvalue
-                    self.message('display %s: %r  [old: %r]' %
-                                 (expr, newvalue, oldvalue))
+                    self.message('display %s: %s  [old: %s]' %
+                                 (expr, self._safe_repr(newvalue, expr),
+                                  self._safe_repr(oldvalue, expr)))
 
     def interaction(self, frame, traceback):
         # Restore the previous signal handler at the Pdb prompt.
@@ -1221,7 +1222,7 @@ def do_args(self, arg):
         for i in range(n):
             name = co.co_varnames[i]
             if name in dict:
-                self.message('%s = %r' % (name, dict[name]))
+                self.message('%s = %s' % (name, self._safe_repr(dict[name], name)))
             else:
                 self.message('%s = *** undefined ***' % (name,))
     do_a = do_args
@@ -1231,7 +1232,7 @@ def do_retval(self, arg):
         Print the return value for the last return of a function.
         """
         if '__return__' in self.curframe_locals:
-            self.message(repr(self.curframe_locals['__return__']))
+            self.message(self._safe_repr(self.curframe_locals['__return__'], "retval"))
         else:
             self.error('Not yet returned!')
     do_rv = do_retval
@@ -1268,6 +1269,12 @@ def _msg_val_func(self, arg, func):
         except:
             self._error_exc()
 
+    def _safe_repr(self, obj, expr):
+        try:
+            return repr(obj)
+        except Exception as e:
+            return _rstr(f"*** repr({expr}) failed: {self._format_exc(e)} ***")
+
     def do_p(self, arg):
         """p expression
         Print the value of the expression.
@@ -1438,12 +1445,12 @@ def do_display(self, arg):
         """
         if not arg:
             self.message('Currently displaying:')
-            for item in self.displaying.get(self.curframe, {}).items():
-                self.message('%s: %r' % item)
+            for key, val in self.displaying.get(self.curframe, {}).items():
+                self.message('%s: %s' % (key, self._safe_repr(val, key)))
         else:
             val = self._getval_except(arg)
             self.displaying.setdefault(self.curframe, {})[arg] = val
-            self.message('display %s: %r' % (arg, val))
+            self.message('display %s: %s' % (arg, self._safe_repr(val, arg)))
 
     complete_display = _complete_expression
 
@@ -1645,6 +1652,8 @@ def _run(self, target: Union[_ModuleTarget, _ScriptTarget]):
 
         self.run(target.code)
 
+    def _format_exc(self, exc: BaseException):
+        return traceback.format_exception_only(exc)[-1].strip()
 
     def _getsourcelines(self, obj):
         # GH-103319

Lib/test/test_pdb.py

@@ -1704,6 +1704,53 @@ def test_pdb_issue_gh_103225():
     (Pdb) continue
     """
 
+def test_pdb_issue_gh_65052():
+    """See GH-65052
+
+    args, retval and display should not crash if the object is not displayable
+    >>> class A:
+    ...     def __new__(cls):
+    ...         import pdb; pdb.Pdb(nosigint=True, readrc=False).set_trace()
+    ...         return object.__new__(cls)
+    ...     def __init__(self):
+    ...         import pdb; pdb.Pdb(nosigint=True, readrc=False).set_trace()
+    ...         self.a = 1
+    ...     def __repr__(self):
+    ...         return self.a
+
+    >>> def test_function():
+    ...     A()
+    >>> with PdbTestInput([  # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
+    ...     's',
+    ...     'retval',
+    ...     'continue',
+    ...     'args',
+    ...     'display self',
+    ...     'display',
+    ...     'continue',
+    ... ]):
+    ...    test_function()
+    > <doctest test.test_pdb.test_pdb_issue_gh_65052[0]>(4)__new__()
+    -> return object.__new__(cls)
+    (Pdb) s
+    --Return--
+    > <doctest test.test_pdb.test_pdb_issue_gh_65052[0]>(4)__new__()-><A instance at ...>
+    -> return object.__new__(cls)
+    (Pdb) retval
+    *** repr(retval) failed: AttributeError: 'A' object has no attribute 'a' ***
+    (Pdb) continue
+    > <doctest test.test_pdb.test_pdb_issue_gh_65052[0]>(7)__init__()
+    -> self.a = 1
+    (Pdb) args
+    self = *** repr(self) failed: AttributeError: 'A' object has no attribute 'a' ***
+    (Pdb) display self
+    display self: *** repr(self) failed: AttributeError: 'A' object has no attribute 'a' ***
+    (Pdb) display
+    Currently displaying:
+    self: *** repr(self) failed: AttributeError: 'A' object has no attribute 'a' ***
+    (Pdb) continue
+    """
+
 
 @support.requires_subprocess()
 class PdbTestCase(unittest.TestCase):

Misc/NEWS.d/next/Library/2023-10-09-19-09-32.gh-issue-65052.C2mRlo.rst

@@ -0,0 +1 @@
+Prevent :mod:`pdb` from crashing when trying to display undisplayable objects