Python Prefix Notation Evaluater
Only addressing your last point about the layout of operatorTable, i would use 4 space indentation as according to PEP8-indentation.  

operatorTable = { 
    "+": Operator(2, lambda a,b: a+b),
    "-": Operator(2, lambda a,b: a-b),
    "/": Operator(2, lambda a,b: a/b),
    "*": Operator(2, lambda a,b: a*b),
    "&lt;": Operator(2, lambda a,b: a&lt;b),
    "&gt;": Operator(2, lambda a,b: a&gt;b),
    "_": Operator(1, lambda a: -a),
    "p": Operator(0, lambda: math.pi),
    "e": Operator(0, lambda: math.e),
}


Also note the comma after the last item. This has a small advantage when you use a source control system, when another item is added after the last item only the new line will show up in a diff and not the previous line which only has a comma added.