Patch #750542: pprint now will pretty print subclasses of list, tuple

and dict too, as long as they don't overwrite __repr__().

Lib/pprint.py

@@ -90,9 +90,9 @@ class PrettyPrinter:
         """
         indent = int(indent)
         width = int(width)
-        assert indent >= 0
+        assert indent >= 0, "indent must be >= 0"
         assert depth is None or depth > 0, "depth must be > 0"
-        assert width
+        assert width, "width must be != 0"
         self._depth = depth
         self._indent_per_level = indent
         self._width = width
@@ -130,7 +130,8 @@ class PrettyPrinter:
         write = stream.write
 
         if sepLines:
-            if typ is dict:
+            r = typ.__repr__
+            if issubclass(typ, dict) and r is dict.__repr__:
                 write('{')
                 if self._indent_per_level > 1:
                     write((self._indent_per_level - 1) * ' ')
@@ -157,8 +158,9 @@ class PrettyPrinter:
                 write('}')
                 return
 
-            if typ is list or typ is tuple:
-                if typ is list:
+            if (issubclass(typ, list) and r is list.__repr__) or \
+               (issubclass(typ, tuple) and r is tuple.__repr__):
+                if issubclass(typ, list):
                     write('[')
                     endchar = ']'
                 else:
@@ -179,7 +181,7 @@ class PrettyPrinter:
                                           allowance + 1, context, level)
                     indent = indent - self._indent_per_level
                     del context[objid]
-                if typ is tuple and length == 1:
+                if issubclass(typ, tuple) and length == 1:
                     write(',')
                 write(endchar)
                 return
@@ -226,7 +228,8 @@ def _safe_repr(object, context, maxlevels, level):
                 write(qget(char, `char`[1:-1]))
         return ("%s%s%s" % (closure, sio.getvalue(), closure)), True, False
 
-    if typ is dict:
+    r = typ.__repr__
+    if issubclass(typ, dict) and r is dict.__repr__:
         if not object:
             return "{}", True, False
         objid = _id(object)
@@ -251,8 +254,9 @@ def _safe_repr(object, context, maxlevels, level):
         del context[objid]
         return "{%s}" % _commajoin(components), readable, recursive
 
-    if typ is list or typ is tuple:
-        if typ is list:
+    if (issubclass(typ, list) and r is list.__repr__) or \
+       (issubclass(typ, tuple) and r is tuple.__repr__):
+        if issubclass(typ, list):
             if not object:
                 return "[]", True, False
             format = "[%s]"

Lib/test/test_pprint.py

@@ -8,6 +8,22 @@ except NameError:
     def uni(x):
         return x
 
+# list, tuple and dict subclasses that do or don't overwrite __repr__
+class list2(list):
+    pass
+class list3(list):
+    def __repr__(self):
+        return list.__repr__(self)
+class tuple2(tuple):
+    pass
+class tuple3(tuple):
+    def __repr__(self):
+        return tuple.__repr__(self)
+class dict2(dict):
+    pass
+class dict3(dict):
+    def __repr__(self):
+        return dict.__repr__(self)
 
 class QueryTestCase(unittest.TestCase):
 
@@ -84,11 +100,20 @@ class QueryTestCase(unittest.TestCase):
                    "expected not isreadable for " + `unreadable`)
 
     def test_same_as_repr(self):
-        # Simple objects and small containers that should be same as repr()
+        # Simple objects, small containers and classes that overwrite __repr__
+        # For those the result should be the same as repr()
         verify = self.assert_
-        for simple in (0, 0L, 0+0j, 0.0, "", uni(""), (), [], {}, verify, pprint,
+        for simple in (0, 0L, 0+0j, 0.0, "", uni(""),
+                       (), tuple2(), tuple3(),
+                       [], list2(), list3(),
+                       {}, dict2(), dict3(),
+                       verify, pprint,
                        -6, -6L, -6-6j, -1.5, "x", uni("x"), (3,), [3], {3: 6},
                        (1,2), [3,4], {5: 6, 7: 8},
+                       tuple2((1,2)), tuple3((1,2)), tuple3(range(100)),
+                       [3,4], list2([3,4]), list3([3,4]), list3(range(100)),
+                       {5: 6, 7: 8}, dict2({5: 6, 7: 8}), dict3({5: 6, 7: 8}),
+                       dict3([(x,x) for x in range(100)]),
                        {"xy\tab\n": (3,), 5: [[]], (): {}},
                        range(10, -11, -1)
                       ):
@@ -99,7 +124,6 @@ class QueryTestCase(unittest.TestCase):
                 verify(native == got, "expected %s got %s from pprint.%s" %
                                       (native, got, function))
 
-
     def test_basic_line_wrap(self):
         # verify basic line-wrapping operation
         o = {'RPM_cal': 0,
@@ -117,7 +141,18 @@ class QueryTestCase(unittest.TestCase):
  'main_code_runtime_us': 0,
  'read_io_runtime_us': 0,
  'write_io_runtime_us': 43690}"""
-        self.assertEqual(pprint.pformat(o), exp)
+        for type in [dict, dict2]:
+            self.assertEqual(pprint.pformat(type(o)), exp)
+
+        o = range(100)
+        exp = '[%s]' % ',\n '.join(map(str, o))
+        for type in [list, list2]:
+            self.assertEqual(pprint.pformat(type(o)), exp)
+
+        o = tuple(range(100))
+        exp = '(%s)' % ',\n '.join(map(str, o))
+        for type in [tuple, tuple2]:
+            self.assertEqual(pprint.pformat(type(o)), exp)
 
     def test_subclassing(self):
         o = {'names with spaces': 'should be presented using repr()',

Misc/NEWS

@@ -170,6 +170,9 @@ Extension modules
 Library
 -------
 
+- Patch #750542: pprint now will pretty print subclasses of list, tuple
+  and dict too, as long as they don't overwrite __repr__().
+
 - Bug #848614: distutils' msvccompiler fails to find the MSVC6
   compiler because of incomplete registry entries.