python 2 coercion

[Terry Reedy]

>What happens (on the C level) if the python interpreter executes
>a statement like
>if <some strange extension type> == None:

For Jython, there is no C level ;-)  For CPython, the beginning point for 
such a question is the byte code (this is 2.2, but should be same in 2.3, 
but you can check):

>>> def equalNone(a): return a == None
...
>>> import dis
>>> dis.dis(equalNone)
          0 SET_LINENO               1

          3 SET_LINENO               1
          6 LOAD_FAST                0 (a)
          9 LOAD_GLOBAL              1 (None)
         12 COMPARE_OP               2 (==)
         15 RETURN_VALUE
         16 LOAD_CONST               0 (None)
         19 RETURN_VALUE

Now go to ceval.c, find the COMPARE_OP branch in the master switch 
statement, and see what gets called.  Note that at this point, the 
interpreter has no idea what is bound to 'a'.

Terry J. Reedy