optimization with the "compiler" module

[Skip Montanaro]

    Andrew> Suppose you have

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

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

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

This is a trivial peephole optimization.  If two constants are summed, they
will appear in the bytecode like

    LOAD_CONST 3
    LOAD_CONST 7.0
    BINARY_ADD

You recognize the pattern, perform the optimization, and move on.

In your example, it would look like

    LOAD_GLOBAL x
    LOAD_CONST 3
    BINARY_ADD
    LOAD_CONST 7.0
    BINARY_ADD

The pattern (const, const, add) never turns up in the instruction stream.

Details here:

    http://manatee.mojam.com/~skip/python/spam7/optimizer.html

Skip