[Python-Dev] Re: native code compiler? (or, OCaml vs. Python)

[Guido van Rossum]

>     Guido> I was thinking of adding appropriate new opcodes for a few
>     Guido> builtins that are called a lot, like len.  This would be
>     Guido> implemented using something like this:
> 
>     Guido>              case BUILTIN_LEN:
>     ...
> 
> Would you special case those calls so that, in effect, __builtin__.len
> couldn't be overridden by a "len" object in the globals or locals?

No, I would only generate a BUILTIN_LEN opcode if there was no local
or global variable 'len'.

A few days ago I proposed a restriction on assigning to an attribute
of a module that stores a new name in that module that is the same as
the name of a built-in; that was meant to outlaw people doing ugly
stuff like

   import random
   random.len = lambda x: len(x)-1
   print random.choice([1,2,3])

and expecting to affect the implementation of choice().

I don't think anybody would do this on purpose (or even by accident),
but the possibility exists, and I'd prefer to live without lying awake
about that case.

(We could make random.__dict__ read-only, like the new-style class
__dict__, if you worry about other ways of stuffing unexpected
variables inside it.  We could also avoid the optimization if there's
an exec statement anywhere in a module, since one could exec code that
says

  import __builtin__
  global len
  len = lambda x: __builtin__.len(x)-1

or one could find another way of outlawing such abominations
(including simply declaring that one shouldn't do that).

--Guido van Rossum (home page: http://www.python.org/~guido/)