overloading for ladder logic

[jimzat at gmail.com]

I am trying to simulate the execution of some PLC ladder logic in
python.

I manually modified the rungs and executed this within python as a
proof of concept, but I'd like to be able to skip the  modification
step.  My thought was that this might be able to be completed via
overloading, but I am not sure if (or how) it could be done.

overloadings:
    + ==> OR
    * ==> AND
    / ==> NOT

Example original code:
     A=/B+C*D
translates to:
    A=not B or C and D

I tried
    def __add__ (a,b):
        return (a or b)

which gives me this:

    >>> x=False
    >>> y=True
    >>> x+y
        1
    >>> x=True
    >>> x+y
        2

How can this be done?