pretty-rendering for os.environ by default

it's dict-like, but not a dict so doesn't get caught by the default dict printer

IPython/lib/pretty.py

@@ -77,11 +77,13 b' Inheritance diagram:'
             Portions (c) 2009 by Robert Kern.
 :license: BSD License.
 """
+
 from contextlib import contextmanager
+import datetime
+import os
+import re
 import sys
 import types
-import re
-import datetime
 from collections import deque
 from io import StringIO
 from warnings import warn
@@ -742,7 +744,6 b' _type_pprinters = {'
     tuple:                      _seq_pprinter_factory('(', ')'),
     list:                       _seq_pprinter_factory('[', ']'),
     dict:                       _dict_pprinter_factory('{', '}'),
-    
     set:                        _set_pprinter_factory('{', '}'),
     frozenset:                  _set_pprinter_factory('frozenset({', '})'),
     super:                      _super_pprint,
@@ -751,12 +752,17 b' _type_pprinters = {'
     types.FunctionType:         _function_pprint,
     types.BuiltinFunctionType:  _function_pprint,
     types.MethodType:           _repr_pprint,
-    
     datetime.datetime:          _repr_pprint,
     datetime.timedelta:         _repr_pprint,
     _exception_base:            _exception_pprint
 }
 
+# render os.environ like a dict
+_env_type = type(os.environ)
+# future-proof in case os.environ becomes a plain dict?
+if _env_type is not dict:
+    _type_pprinters[_env_type] = _dict_pprinter_factory('environ{', '}')
+
 try:
     # In PyPy, types.DictProxyType is dict, setting the dictproxy printer
     # using dict.setdefault avoids overwritting the dict printer
@@ -768,7 +774,7 b' except AttributeError: # Python 3'
     _type_pprinters[types.MappingProxyType] = \
         _dict_pprinter_factory('mappingproxy({', '})')
     _type_pprinters[slice] = _repr_pprint
-    
+
 try:
     _type_pprinters[long] = _repr_pprint
     _type_pprinters[unicode] = _repr_pprint

IPython/lib/tests/test_pretty.py

@@ -6,6 +6,7 b''
 
 
 from collections import Counter, defaultdict, deque, OrderedDict
+import os
 import types
 import string
 import unittest
@@ -406,6 +407,15 b' def test_mappingproxy():'
     for obj, expected in cases:
         nt.assert_equal(pretty.pretty(obj), expected)
 
+
+def test_pretty_environ():
+    dict_repr = pretty.pretty(dict(os.environ))
+    # reindent to align with 'environ' prefix
+    dict_indented = dict_repr.replace('\n', '\n' + (' ' * len('environ')))
+    env_repr = pretty.pretty(os.environ)
+    nt.assert_equals(env_repr, 'environ' + dict_indented)
+
+
 def test_function_pretty():
     "Test pretty print of function"
     # posixpath is a pure python module, its interface is consistent