Issue #23502: The pprint module now supports mapping proxies.

In particular the __dict__ attributes of building types.

Lib/pprint.py

@@ -36,6 +36,7 @@ saferepr()
 
 import re
 import sys as _sys
+import types as _types
 from collections import OrderedDict as _OrderedDict
 from io import StringIO as _StringIO
 
@@ -313,6 +314,14 @@ class PrettyPrinter:
 
     _dispatch[bytearray.__repr__] = _pprint_bytearray
 
+    def _pprint_mappingproxy(self, object, stream, indent, allowance, context, level):
+        stream.write('mappingproxy(')
+        self._format(object.copy(), stream, indent + 13, allowance + 1,
+                     context, level)
+        stream.write(')')
+
+    _dispatch[_types.MappingProxyType.__repr__] = _pprint_mappingproxy
+
     def _format_dict_items(self, items, stream, indent, allowance, context,
                            level):
         write = stream.write

Lib/test/test_pprint.py

@@ -7,6 +7,7 @@ import test.test_set
 import random
 import collections
 import itertools
+import types
 
 # list, tuple and dict subclasses that do or don't overwrite __repr__
 class list2(list):
@@ -271,6 +272,34 @@ class QueryTestCase(unittest.TestCase):
  'a': 6,
  'lazy': 7,
  'dog': 8}""")
+
+    def test_mapping_proxy(self):
+        words = 'the quick brown fox jumped over a lazy dog'.split()
+        d = dict(zip(words, itertools.count()))
+        m = types.MappingProxyType(d)
+        self.assertEqual(pprint.pformat(m), """\
+mappingproxy({'a': 6,
+              'brown': 2,
+              'dog': 8,
+              'fox': 3,
+              'jumped': 4,
+              'lazy': 7,
+              'over': 5,
+              'quick': 1,
+              'the': 0})""")
+        d = collections.OrderedDict(zip(words, itertools.count()))
+        m = types.MappingProxyType(d)
+        self.assertEqual(pprint.pformat(m), """\
+mappingproxy({'the': 0,
+              'quick': 1,
+              'brown': 2,
+              'fox': 3,
+              'jumped': 4,
+              'over': 5,
+              'a': 6,
+              'lazy': 7,
+              'dog': 8})""")
+
     def test_subclassing(self):
         o = {'names with spaces': 'should be presented using repr()',
              'others.should.not.be': 'like.this'}

Misc/NEWS

@@ -26,6 +26,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #23502: The pprint module now supports mapping proxies.
+
 - Issue #17530: pprint now wraps long bytes objects and bytearrays.
 
 - Issue #22687: Fixed some corner cases in breaking words in tetxtwrap.