gh-132855: Use overridden custom format for inherited PrettyPrinter

Author: Agent-Hellboy

Lib/pprint.py

@@ -181,30 +181,51 @@ def _format(self, object, stream, indent, allowance, context, level):
             self._recursive = True
             self._readable = False
             return
+
+        # If this is a subclass of PrettyPrinter, force all known
+        # container types through their pretty-printers so that any
+        # override of format() applies to their elements.
+        if type(self) is not PrettyPrinter:
+            fn = type(object).__repr__
+            # skip raw repr for str/bytes
+            if fn in self._dispatch and not isinstance(object, (str, bytes, bytearray)):
+                context[objid] = 1
+                self._dispatch[fn](
+                    self, object, stream,
+                    indent, allowance, context, level + 1
+                )
+                del context[objid]
+                return
+
+        # fallback to one-line repr + width 
         rep = self._repr(object, context, level)
         max_width = self._width - indent - allowance
         if len(rep) > max_width:
             p = self._dispatch.get(type(object).__repr__, None)
-            # Lazy import to improve module import time
             from dataclasses import is_dataclass
 
             if p is not None:
                 context[objid] = 1
-                p(self, object, stream, indent, allowance, context, level + 1)
+                p(self, object, stream,
+                  indent, allowance, context, level + 1)
                 del context[objid]
                 return
-            elif (is_dataclass(object) and
-                  not isinstance(object, type) and
-                  object.__dataclass_params__.repr and
-                  # Check dataclass has generated repr method.
-                  hasattr(object.__repr__, "__wrapped__") and
-                  "__create_fn__" in object.__repr__.__wrapped__.__qualname__):
+            elif (is_dataclass(object)
+                  and not isinstance(object, type)
+                  and object.__dataclass_params__.repr
+                  and hasattr(object.__repr__, "__wrapped__")
+                  and "__create_fn__" in object.__repr__.__wrapped__.__qualname__):
                 context[objid] = 1
-                self._pprint_dataclass(object, stream, indent, allowance, context, level + 1)
+                self._pprint_dataclass(object, stream,
+                                       indent, allowance,
+                                       context, level + 1)
                 del context[objid]
                 return
+
+        # write the one-line repr
         stream.write(rep)
 
+
     def _pprint_dataclass(self, object, stream, indent, allowance, context, level):
         # Lazy import to improve module import time
         from dataclasses import fields as dataclass_fields

Lib/test/test_pprint.py

@@ -1136,6 +1136,38 @@ def format(self, object, context, maxlevels, level):
             return pprint.PrettyPrinter.format(
                 self, object, context, maxlevels, level)
 
+# Issue 132855
+SENTINAL = object()
+class _hashable:
+    def __hash__(self):
+        return 1
+
+HASHABLE_SENTINAL = _hashable()
+class CustomPrettyPrinter(pprint.PrettyPrinter):
+    def format(self, obj, context, maxlevels, level):
+        if obj is SENTINAL:
+            return "SENTINAL", True, False
+        elif obj is HASHABLE_SENTINAL:
+            return "HASHABLE_SENTINAL", True, False
+        else:
+            return super().format(obj, context, maxlevels, level)
+    
+class CustomPrettyPrinterTest(unittest.TestCase):
+    def test_custom_printer(self):
+        # Test that the custom printer works as expected
+        obj = SENTINAL
+        formatted = CustomPrettyPrinter().pformat(obj)
+        self.assertEqual(formatted, "SENTINAL")
+        
+        obj = HASHABLE_SENTINAL
+        formatted = CustomPrettyPrinter().pformat(obj)
+        self.assertEqual(formatted, "HASHABLE_SENTINAL")
+        
+        # Test that the default printer works as expected
+        obj = object()
+        formatted = pprint.pformat(obj)
+        self.assertNotEqual(formatted, "SENTINAL")
+        self.assertNotEqual(formatted, "HASHABLE_SENTINAL")
 
 if __name__ == "__main__":
     unittest.main()