> I determined that 'raise TypeError' and 'return NotImplemented' both
> result in the call of the reflected method

Are you sure?  raise TypeError *should* result in the operation being abandoned, with the reflected operation not tried.


Python 3.3.0rc2+ (default:3504cbb3e1d8, Sep 20 2012, 22:08:44) 
[GCC 4.2.1 (Apple Inc. build 5664)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class A:
...     def __add__(self, other):
...         raise TypeError("Don't know how to add")
...     def __le__(self, other):
...         raise TypeError("Can't compare")
... 
[65945 refs]
>>> class B:
...     def __radd__(self, other):
...         return 42
...     def __ge__(self, other):
...         return False
... 
[66016 refs]
>>> A() <= B()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 5, in __le__
TypeError: Can't compare
[66064 refs]
>>> A() + B()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __add__
TypeError: Don't know how to add
[66065 refs]