[Python-Dev] Adding a builtins parameter to eval(), exec() and __import__().

[Nick Coghlan]

On Thu, Mar 8, 2012 at 11:40 PM, Mark Shannon <mark at hotpy.org> wrote:
> Other code will use whatever builtins they were given at __import__.

Then they're not builtins - they're module-specific chained globals.
The thing that makes the builtins special is *who else* can see them
(i.e. all the other code in the process). If you replace
builtins.open, you replace if for everyone (that hasn't either
shadowed it or cached a reference to the original).

> The key point is that every piece of code already inherits locals, globals
> and builtins from somewhere else.
> We can already control locals (by which parameters are passed in) and
> globals via exec, eval, __import__, and runpy (any others?)
> but we can't control builtins.

Correct - because controlling builtins is the domain of sandboxes.

> One last point is that this is a low-impact change. All code using eval,
> etc. will continue to work as before.
> It also may speed things up a little.

Passing in a ChainMap instance as the globals when you want to include
an additional namespace in the lookup chain is even lower impact.

A reference implementation and concrete use cases might change my
mind, but for now, I'm just seeing a horrendously complicated approach
with huge implications for the runtime data model semantics for
something that 3.3 already supports in a much simpler fashion.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia