diff --git a/Lib/os.py b/Lib/os.py
index 8b7876c7a..8c19a89c6 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -1,34 +1,56 @@
 from _os import *
 
-class _Environ():
-    def __init__(self, data, putenv, unsetenv):
+# Change environ to automatically call putenv(), unsetenv if they exist.
+from _collections_abc import MutableMapping
+
+class _Environ(MutableMapping):
+    def __init__(self, data, encodekey, decodekey, encodevalue, decodevalue, putenv, unsetenv):
+        self.encodekey = encodekey
+        self.decodekey = decodekey
+        self.encodevalue = encodevalue
+        self.decodevalue = decodevalue
         self.putenv = putenv
         self.unsetenv = unsetenv
         self._data = data
 
     def __getitem__(self, key):
-        return self._data[key]
+        try:
+            value = self._data[self.encodekey(key)]
+        except KeyError:
+            # raise KeyError with the original key value
+            # raise KeyError(key) from None
+            raise KeyError(key)
+
+        return self.decodevalue(value)
 
     def __setitem__(self, key, value):
+        key = self.encodekey(key)
+        value = self.encodevalue(value)
         self.putenv(key, value)
         self._data[key] = value
 
     def __delitem__(self, key):
-        self.unsetenv(key)
-        del self._data[key]
+        encodedkey = self.encodekey(key)
+        self.unsetenv(encodedkey)
+        try:
+            del self._data[encodedkey]
+        except KeyError:
+            # raise KeyError with the original key value
+            # raise KeyError(key) from None
+            raise KeyError(key)
 
     def __iter__(self):
         # list() from dict object is an atomic operation
         keys = list(self._data)
         for key in keys:
-            yield key
+            yield self.decodekey(key)
 
     def __len__(self):
         return len(self._data)
 
     def __repr__(self):
         return 'environ({{{}}})'.format(', '.join(
-            ('{}: {}'.format(key, value)
+            ('{!r}: {!r}'.format(self.decodekey(key), self.decodevalue(value))
             for key, value in self._data.items())))
 
     def copy(self):
@@ -39,13 +61,62 @@ class _Environ():
             self[key] = value
         return self[key]
 
-environ = _Environ(environ, putenv, unsetenv)
+try:
+    _putenv = putenv
+except NameError:
+    _putenv = lambda key, value: None
+# else:
+#     if "putenv" not in __all__:
+#         __all__.append("putenv")
+
+try:
+    _unsetenv = unsetenv
+except NameError:
+    _unsetenv = lambda key: _putenv(key, "")
+# else:
+#     if "unsetenv" not in __all__:
+#         __all__.append("unsetenv")
+
+def _createenviron():
+    # if name == 'nt':
+    #     # Where Env Var Names Must Be UPPERCASE
+    #     def check_str(value):
+    #         if not isinstance(value, str):
+    #             raise TypeError("str expected, not %s" % type(value).__name__)
+    #         return value
+    #     encode = check_str
+    #     decode = str
+    #     def encodekey(key):
+    #         return encode(key).upper()
+    #     data = {}
+    #     for key, value in environ.items():
+    #         data[encodekey(key)] = value
+    # else:
+    #     # Where Env Var Names Can Be Mixed Case
+    #     encoding = sys.getfilesystemencoding()
+    #     def encode(value):
+    #         if not isinstance(value, str):
+    #             raise TypeError("str expected, not %s" % type(value).__name__)
+    #         return value.encode(encoding, 'surrogateescape')
+    #     def decode(value):
+    #         return value.decode(encoding, 'surrogateescape')
+    #     encodekey = encode
+    decode = str
+    encode = str
+    encodekey = encode
+    data = environ
+    return _Environ(data,
+        encodekey, decode,
+        encode, decode,
+        _putenv, _unsetenv)
+
+# unicode environ
+environ = _createenviron()
+del _createenviron
+
 
 def getenv(key, default=None):
     """Get an environment variable, return None if it doesn't exist.
     The optional second argument can specify an alternate default.
     key, default and the result are str."""
-    try:
-        return environ[key]
-    except KeyError:
-        return default
+    return environ.get(key, default)