pyderasn.py | 27 ++++++++++++++++-----------

diff --git a/pyderasn.py b/pyderasn.py
index d41b0a4b4bbe51a385eb564c86807e4d8c83e4be9e8e4a7b1cb5e97bb049e610..ef4146be4d705b169271ecc2c582231071981ed0cee66e360ac1f00617796fea 100755
--- a/pyderasn.py
+++ b/pyderasn.py
@@ -555,6 +555,8 @@ from six import indexbytes
 from six import int2byte
 from six import integer_types
 from six import iterbytes
+from six import iteritems
+from six import itervalues
 from six import PY2
 from six import string_types
 from six import text_type
@@ -1861,7 +1863,7 @@         return self._value < their._value
 
     @property
     def named(self):
-        for name, value in self.specs.items():
+        for name, value in iteritems(self.specs):
             if value == self._value:
                 return name
 
@@ -2243,7 +2245,7 @@         )
 
     @property
     def named(self):
-        return [name for name, bit in self.specs.items() if self[bit]]
+        return [name for name, bit in iteritems(self.specs) if self[bit]]
 
     def __call__(
             self,
@@ -3355,7 +3357,7 @@     def _value_sanitize(self, value):
         if isinstance(value, self.__class__):
             value = value._value
         elif isinstance(value, integer_types):
-            for _value in self.specs.values():
+            for _value in itervalues(self.specs):
                 if _value == value:
                     break
             else:
@@ -4067,7 +4069,7 @@         self._assert_ready()
         return self._value[1].encode()
 
     def _decode(self, tlv, offset, decode_path, ctx, tag_only):
-        for choice, spec in self.specs.items():
+        for choice, spec in iteritems(self.specs):
             sub_decode_path = decode_path + (choice,)
             try:
                 spec.decode(
@@ -4552,7 +4554,7 @@                 self._value = default_obj.copy()._value
 
     @property
     def ready(self):
-        for name, spec in self.specs.items():
+        for name, spec in iteritems(self.specs):
             value = self._value.get(name)
             if value is None:
                 if spec.optional:
@@ -4567,7 +4569,7 @@     @property
     def bered(self):
         if self.expl_lenindef or self.lenindef or self.ber_encoded:
             return True
-        return any(value.bered for value in self._value.values())
+        return any(value.bered for value in itervalues(self._value))
 
     def copy(self):
         obj = self.__class__(schema=self.specs)
@@ -4581,7 +4583,7 @@         obj.vlen = self.vlen
         obj.expl_lenindef = self.expl_lenindef
         obj.lenindef = self.lenindef
         obj.ber_encoded = self.ber_encoded
-        obj._value = {k: v.copy() for k, v in self._value.items()}
+        obj._value = {k: v.copy() for k, v in iteritems(self._value)}
         return obj
 
     def __eq__(self, their):
@@ -4642,7 +4644,7 @@         return None
 
     def _encoded_values(self):
         raws = []
-        for name, spec in self.specs.items():
+        for name, spec in iteritems(self.specs):
             value = self._value.get(name)
             if value is None:
                 if spec.optional:
@@ -4708,7 +4710,7 @@         sub_offset = offset + tlen + llen
         values = {}
         ber_encoded = False
         ctx_allow_default_values = ctx.get("allow_default_values", False)
-        for name, spec in self.specs.items():
+        for name, spec in iteritems(self.specs):
             if spec.optional and (
                     (lenindef and v[:EOC_LEN].tobytes() == EOC) or
                     len(v) == 0
@@ -4902,6 +4904,9 @@         raws.sort()
         v = b"".join(raws)
         return b"".join((self.tag, len_encode(len(v)), v))
 
+    def _specs_items(self):
+        return iteritems(self.specs)
+
     def _decode(self, tlv, offset, decode_path, ctx, tag_only):
         try:
             t, tlen, lv = tag_strip(tlv)
@@ -4956,11 +4961,11 @@         ber_encoded = False
         ctx_allow_default_values = ctx.get("allow_default_values", False)
         ctx_allow_unordered_set = ctx.get("allow_unordered_set", False)
         value_prev = memoryview(v[:0])
-        specs_items = self.specs.items
+
         while len(v) > 0:
             if lenindef and v[:EOC_LEN].tobytes() == EOC:
                 break
-            for name, spec in specs_items():
+            for name, spec in self._specs_items():
                 sub_decode_path = decode_path + (name,)
                 try:
                     spec.decode(