[Python-Dev] xmlrpclib.{True, False} (was Re: Assignment to None)

[Thomas Lee]

My work on the AST optimizer has led me down the path of attempting to 
replace things like Name("True") with Const(Py_True) nodes. This works 
fine most of the time, with the exception of the xmlrpclib module, where 
True and False are actually redefined:

    True, False = True, False

As I stated in an earlier email, the optimizer tries to replace the 
tuple of Name nodes on the LHS with Py_True and Py_False respectively, 
which has the net effect of removing xmlrpclib.{True, False}. Obviously 
undesirable.

The simplest options I can think of to remedy this:

1. A setattr hack: setattr(__import__(__name__), "True", True)
2. Remove all optimization of Name("True") and Name("False")
3. Skip AST optimization entirely for the LHS of Assignment nodes 
(effectively removing any optimization of the "targets" tuple)

I'm leaning towards #3 at the moment as it seems like it's going to be 
the cleanest approach and makes a lot of sense -- at least on the 
surface. Can anybody think of problems with this approach?

Cheers,
T

Thomas Lee wrote:
> Martin v. Löwis wrote:
>>> The question is, what is the specification for Python.
>>>     
>>
>> Now, that's a more interesting question than the question originally
>> asked (which I interpreted as "why does it work the way it works").
>>
>> The only indication in the specification of that feature I could find
>> was:
>>
>> http://docs.python.org/dev/library/constants.html
>>
>> "Changed in version 2.4: Assignments to None are illegal and raise a
>> SyntaxError."
>>
>> Now, given that this talks about the built-in namespace, this *doesn't*
>> specify that foo.None=1 should also raise a syntax error.
>>
>> So the implementation apparently deviates from the specification.
>>
>> In Python 3, None, True, and False are keywords, so clearly, the
>> intended semantics is also the implemented one (and the language
>> description for 2.x needs to be updated/clarified).
>>
>>   
> Interestingly enough, the semantics of True, False and None are 
> different from one another in 2.6:
>
> True = "blah" and False = 6 are perfectly legal in Python <=2.6.
>
> Funny, I just ran into this. I was trying to figure out why the AST 
> optimization code was breaking test_xmlrpc ... turns out xmlrpclib 
> defines xmlrpclib.True and xmlrpclib.False and the optimizer was 
> trying to resolve them as constants while compiling the module. Ouch.
>
> What happened in 3k? Were the constants in xmlrpclib renamed/removed?
>
> Cheers,
> T
>
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