optimization with the "compiler" module

[Andrew Dalke]

sean.bowman at acm.org:
>I'm wondering if there's a way to optimize code generated using the
>compiler module.  for example, if I say::
>
> import dis
> from parser import compileast, expr
>
> code = compileast(expr('x+3+7.'))
> print dis.dis(code)
>
>I notice that the constants aren't folded.  is there a way to do this, or
>do I have to fiddle with the ast myself?

Suppose you have

class Strange:
    def __add__(self, other):
        return self
x = Strange()

Then x+3+7.0 = (x+3)+7.0 = x+7.0 = x

The compiler can't know what 'x' might be so can't fold constants
in this case.  You could if it was '3+7.0+x'.

One advantage to Python is that incorrect constant folding has
never caused a bug in user code.  Compare this to C compilers where
I've had plenty of troubles with the optimizer.  The Python
implementation leans more towards simple than squeeze out performance
 -- the latter can be done either with hand optimization or switching
to C.
                    Andrew
                    dalke at dalkescientific.com