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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