Built-in odict is a lifted type for now (i.e. we do not wrap it in an EPyObject).

Author: cdleary

README.md

@@ -72,6 +72,20 @@ To run a specific test via `tox` on a specific Python version:
 PYTEST_ARGS=-ktry_except_raise tox -e py37
 ```
 
+### OS X Multiple Python Versions
+
+On OS X multiple Python versions can be installed via `pyenv`; something along
+the lines of:
+
+```
+$ pyenv install 3.7
+$ echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.bash_profile
+$ echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bash_profile
+$ echo 'eval "$(pyenv init --path)"' >> ~/.bash_profile
+$ echo 'eval "$(pyenv init -)"' >> ~/.bash_profile
+$ ln -s $(pyenv which python3.7) /usr/local/bin/python3.7
+```
+
 ### py.test
 
 py.test is run for any given Python version under test -- it is driven via a

src/echo/interp_routines.py

@@ -1,3 +1,4 @@
+import collections
 import operator
 import os
 import sys
@@ -21,23 +22,29 @@
 import termcolor
 
 
+# Many opcodes end up delegating to special functions in the object protocol --
+# this maps bytecode operation names to the corresponding special function
+# name.
 OPNAME_TO_SPECIAL = {
-    'BINARY_SUBTRACT': '__sub__',
     'BINARY_ADD': '__add__',
-    'BINARY_SUBSCR': '__getitem__',
     'BINARY_AND': '__and__',
     'BINARY_MULTIPLY': '__mul__',
     'BINARY_OR': '__or__',
     'BINARY_POWER': '__pow__',
+    'BINARY_SUBSCR': '__getitem__',
+    'BINARY_SUBTRACT': '__sub__',
 }
+# These are the "right hand side" variants of the above for the symmetrical
+# binops.
 OPNAME_TO_SPECIAL_RHS = {
     'BINARY_ADD': '__radd__',
-    'BINARY_SUBTRACT': '__rsub__',
-    'BINARY_MULTIPLY': '__rmul__',
     'BINARY_AND': '__rand__',
+    'BINARY_MULTIPLY': '__rmul__',
     'BINARY_OR': '__ror__',
     'BINARY_POWER': '__rpow__',
+    'BINARY_SUBTRACT': '__rsub__',
 }
+
 COMPARE_TO_SPECIAL = {
     '==': '__eq__',
     '!=': '__ne__',
@@ -139,6 +146,7 @@ def run_binop(opname: Text, lhs: Any, rhs: Any, ictx: ICtx) -> Result[Any]:
     builtin_value_types = {
         ebool, ebytes, estr, eint, elist, edict, ebytearray, eset, etuple,
         float, complex, slice, range, ebytearray, type(sys.version_info),
+        collections.OrderedDict,
     }
 
     if (opname in ('BINARY_TRUE_DIVIDE', 'BINARY_MODULO') and rhs_type is eint